Unusual prompts when game stopped working

I was playing a game with Dialga against a future Box deck. The ! mark flashed on my screen as I was playing, indicating connectivity issues.

I had just returned to the game following the 1009** error interrupting my last gaming experience . As the game was loading up for a second time on my MacBook Air, an error message flashed up saying that my account was open on multiple devices and would close down. It then prompted me to select a language and enter my Pokemon account details. I found this confusing and have therefore decided to report it.

Should I just sign in as normal or is my account getting hacked?