Metronome using Swinging Sphene

Hi, During a game earlier, I used my Clefable's Metronome ability and chose Swinging Sphene from my opponent's Alolan Exeggutor ex. The coin flip was a heads. But for some reason this didn't knock my opponent's pokémon out. Considering it was in the active spot, I don't fully understand whether this is a bug or a strange ruling.

I will enclose the battle log in case anyone wants clarification.

Any help is gratefully appreciated!

Setup
bad_luck69 chose tails for the opening coin flip.
Chessermon won the coin toss.
Chessermon decided to go first.
bad_luck69 drew 7 cards for the opening hand.

• 7 drawn cards.
  Chessermon drew 7 cards for the opening hand.
• 7 drawn cards.
  • Nest Ball, Revavroom, Buddy-Buddy Poffin, Switch, Arven, Arven, Mewtwo ex
  bad_luck69 played Exeggcute to the Active Spot.
  bad_luck69 played Snorunt to the Bench.
  Chessermon played Mewtwo ex to the Active Spot.

Turn # 1 - Chessermon's Turn
Chessermon drew Super Rod.
Chessermon played Nest Ball.

• Chessermon drew Varoom and played it to the Bench.
• Chessermon shuffled their deck.
  Chessermon played Buddy-Buddy Poffin.
• Chessermon drew 2 cards and played them to the Bench.
  • Clefairy, Clefairy
• Chessermon shuffled their deck.
  Chessermon played Switch.
• Chessermon's Clefairy was switched with Chessermon's Mewtwo ex to become the Active Pokémon.
  Chessermon's Clefairy is now in the Active Spot.
  Chessermon's Clefairy used Moon-Watching Party.
• Chessermon attached Basic Psychic Energy to Clefairy on the Bench.
• Chessermon shuffled their deck.
  Chessermon ended their turn.

Turn # 1 - bad_luck69's Turn
bad_luck69 drew a card.
bad_luck69 played Horsea to the Bench.
bad_luck69 attached Basic Grass Energy to Exeggcute in the Active Spot.
bad_luck69 played Calamitous Snowy Mountain to the Stadium spot.
bad_luck69's Exeggcute used Precocious Evolution.

• bad_luck69 evolved Exeggcute to Alolan Exeggutor ex in the Active Spot.
• bad_luck69 shuffled their deck.

Turn # 2 - Chessermon's Turn
Chessermon drew Buddy-Buddy Poffin.
Chessermon played Buddy-Buddy Poffin.

• Chessermon drew 2 cards and played them to the Bench.
  • Clefairy, Marill
• Chessermon shuffled their deck.
  Chessermon's Clefairy used Moon-Watching Party.
• Chessermon attached Basic Psychic Energy to Clefairy on the Bench.
• Chessermon attached Basic Psychic Energy to Clefairy on the Bench.
• Chessermon shuffled their deck.
  Chessermon evolved Varoom to Revavroom on the Bench.
  Chessermon played Arven.
• Chessermon drew 2 cards.
  • Ultra Ball, Hero's Cape
• Chessermon shuffled their deck.
  Chessermon played Ultra Ball.
• Chessermon discarded 2 cards.
  • Super Rod, Arven
• Chessermon drew Clefable.
• Chessermon shuffled their deck.
  Chessermon evolved Clefairy to Clefable on the Bench.
  Chessermon attached Hero's Cape to Clefable on the Bench.
  Chessermon ended their turn.

Turn # 2 - bad_luck69's Turn
bad_luck69 drew a card.
bad_luck69 attached Basic Water Energy to Alolan Exeggutor ex in the Active Spot.
bad_luck69 evolved Snorunt to Froslass ex on the Bench.
bad_luck69's Alolan Exeggutor ex used Tropical Frenzy on Chessermon’s Clefairy for 150 damage.

• bad_luck69 attached Basic Water Energy to Froslass ex on the Bench.
  Chessermon's Clefairy was Knocked Out!
  Chessermon's Clefable is now in the Active Spot.
  bad_luck69 took a Prize card.
  A card was added to bad_luck69's hand.

Turn # 3 - Chessermon's Turn
Chessermon drew Buddy-Buddy Poffin.
Chessermon played Buddy-Buddy Poffin.

• Chessermon drew Varoom and played it to the Bench.
• Chessermon shuffled their deck.
  Chessermon's Clefable used Metronome.
• Chessermon chose Swinging Sphene
• Chessermon flipped a coin and it landed on heads.

Turn # 3 - bad_luck69's Turn
bad_luck69 drew a card.
bad_luck69's Alolan Exeggutor ex used Tropical Frenzy on Chessermon’s Clefable for 150 damage.

Turn # 4 - Chessermon's Turn
Chessermon drew Switch Cart.
Chessermon's Clefable used Metronome.

• Chessermon chose Swinging Sphene
• Chessermon flipped a coin and it landed on tails.
  bad_luck69's Horsea was Knocked Out!
  Chessermon took a Prize card.
  Tulip was added to Chessermon's hand.

Turn # 4 - bad_luck69's Turn
bad_luck69 drew a card.
bad_luck69's Alolan Exeggutor ex used Tropical Frenzy on Chessermon’s Clefable for 150 damage.
Chessermon's Clefable was Knocked Out!

• 4 cards were discarded from Chessermon's Clefable.
  • Basic Psychic Energy, Basic Psychic Energy, Clefairy, Hero's Cape
  Chessermon's Clefairy is now in the Active Spot.
  bad_luck69 took a Prize card.
  A card was added to bad_luck69's hand.

Turn # 5 - Chessermon's Turn
Chessermon drew Basic Psychic Energy.
Chessermon played Tulip.

• Chessermon moved Chessermon's 2 cards to their hand.
  • Clefable, Basic Psychic Energy
  Chessermon attached Basic Psychic Energy to Clefairy in the Active Spot.
  Calamitous Snowy Mountain was activated.
• Chessermon put 2 damage counters on bad_luck69's Clefairy.
  Chessermon evolved Clefairy to Clefable in the Active Spot.
  Chessermon's Revavroom used Rumbling Engine.
• Chessermon discarded Basic Psychic Energy.
• Chessermon drew 5 cards.
  • Buddy-Buddy Poffin, Basic Psychic Energy, Professor's Research, Switch Cart, Basic Psychic Energy
  Chessermon's Clefable used Metronome.
• Chessermon chose Swinging Sphene
• Chessermon flipped a coin and it landed on tails.

Turn # 5 - bad_luck69's Turn
bad_luck69 drew a card.
bad_luck69 attached Basic Water Energy to Froslass ex on the Bench.
bad_luck69's Alolan Exeggutor ex used Tropical Frenzy on Chessermon’s Clefable for 150 damage.
Chessermon's Clefable was Knocked Out!

• 3 cards were discarded from Chessermon's Clefable.
  • Basic Psychic Energy, Basic Psychic Energy, Clefairy
  You conceded. bad_luck69 wins.