I have honestly never heard this phrase in America. It seems like a British slang. It is cool to see British slang on posts here. Even native speakers have room to improve.

This means that you are not the same other people. It is a compliment. People say this if you have some unusual quality. Good luck!

I've heard "rare bird" used in only a rude, "cheeky," condescending way. Calling someone a "rare bird" means the person is weird or unusual, but not in a good way. For example, "she takes a bath once per year!" "Ummm..well, that's a rare bird!"

An exceptional person or thing; a rarity.

珍しい人