I HAVE A QUESTIO N!!!!

okay so do oyu guys think that muscle man and starla form Regular Show are humans or smth else. because I was always like 'man its crazy who the only two green people ever managed to get together' but then my brother said it was because they were the same species and i just Never concideredd that before. this interaction was years ago but i'm pondering on it again now so i must ask. what do you guys think