Isn't that what humans do too? We mimic noises we've heard before and we associate meaning to the noises. Parrots can do that. Our quaker parrot would bite you, then say 'not supposed to bite'. He clearly associated some kind of meaning to that phrase.

Not to make an argument against parrots understanding, but humans understand noises before they mimic them. Children are often able to learn and express themselves in sign language (if taught obviously) earlier than they can learn to speak, and they can respond to spoken word in sign language before they can speak.

Or maybe he just learned that's what people say when he bites them, so he started saying that himself.