That actually stuck out to me as well. He should have shown up with the mask on.
But that would have made it harder for the squid thing to get access to his mouth and face! Which it needed to do so we could see the classic alien at the end!
Another prime example of a scene that makes sense by itself to advance a plot point, but makes no sense in the greater scope of the movie. This movie was filled with scenes like this. Didn't even catch this one in the theater