Ah, the great Clarabelle red herring. This is the crucial evidence where cow Goofy truthers stake their claims. With same-animal characters like Daisy & Donald and Mickey & Minnie being romantic interests, Disney did establish a certain visual formula for audiences to expect.
Naturally, some people make a logical leap to thinking that if Goofy is Clarabelle the Cow’s love interest, then he, too, must be the same species. But this could be true if the earliest shorts didn’t already break their own rules.
In the 1930s, Clarabelle and Horace Horsecollar were engaged for a brief time. He was her love interest for many years until this character fell out of favor and Goofy took the spotlight. Horace Horsecollar was always a horse and a different species from Clarabelle, meaning that Disney does break away from same-species romances. So Goofy doesn’t have to be a cow just based on his connection to Clarabelle.