> His response to the call feels a bit like Michael Scott in the episode Casino Night. "I went all in, you should fold, I have good cards".

You're misunderstanding. His response (and the response from the rest of the poker community) isn't based on any call, it's based on a call with her specific hand. That's the suspicious part (and her behaviour after the hand). Garett has bluffed and been called and lost many times and not accused the other player of cheating.