Wario didn't know that Goose had a last name or a first name or any full name really. He just knew that Goose was named after an annoying, honking bird. Which is why his nickname was bird-brain. (See Wario's puns are hilarious too. Except that wasn't a pun. It was... who knows.)

"I guess so! You sure have the brain of one! Wah ha ha ha!" Wario really needed to find another joke about Goose's name.