@realcaseyrollins haha. I have heard people use they for a squirrel on the sidewalk. Misgendering a squirrel would be terrible.
Its not about misgendering, thats just proper english. They has been used as the gender-neutral singular pronoun since 1375 (first citation in a dictionary). Its literally just the correct term if your speaking english, nothing more. It is not considered proper when discussing animals, that is reserved for inanimate objects (like casey's cup example).
They has plenty of history as a gender neutral si gular back to 1375. As for aninals im not sure when we used they but it obvohsly makes sense since they have sex and is proper engliah today at least.