I can understand someone being mistaken about penguins being birds versus mammals. They'd be pretty funny-looking mammals, but they're already pretty funny-looking birds, and their bird-like qualities aren't really distinguishable in photos and such. It's a little weird for someone to have that confusion about such a well-known animal, but the ridiculous part is confidently asserting the wrong info.
Normally I could see the other guys being roped into believing that a penguin is a mammal if someone was arguing it, because there're a lot of things about taxonomy that have common misconceptions. (For example, people often think mushrooms are plants and ferrets are rodents.) But someone present arguing the truth should have kept them from being confused.