He is, though, because his opinion on Santa Claus should be completely irrelevant to his interactions with his co-workers. But if he prioritizes being hostile by correcting and insulting people over being humble and accepting that others might believe differently, he is being toxic -- he's poisonous to be around.
There are different ways to stand by one's beliefs. One is to keep them to yourself and let them guide your decisions silently, but defend them vigorously if they are actively challenged. And one is to feel the need to rub them into everyone's face constantly, because there is only Right and Wrong and you can't deal with somebody being wrong (i.e., of a different opinion than you) without feeling personally attacked and going on the offensive.
There are different ways to stand by one's beliefs. One is to keep them to yourself and let them guide your decisions silently, but defend them vigorously if they are actively challenged. And one is to feel the need to rub them into everyone's face constantly, because there is only Right and Wrong and you can't deal with somebody being wrong (i.e., of a different opinion than you) without feeling personally attacked and going on the offensive.