What does Horse of a different feather mean?

It's typically a malapropism that is used to add a wry wrinkle to the speaker's overt disinclination to use either of the clichéd metaphors "horse of a different color" or "bird of a different feather."

Also technically a catachresis used either wittingly or not to convey the speaker's opinion that something doesn't quite fit the norm of an object of its type.