"Unexpected pairing" refers to two things or entities that are put together, combined, or connected in a way that is surprising or unusual. Full definition
One of the best parts about fashion in my eyes is that you can throw together unexpected pairs of things and they can still look balanced. (keepcalmandchiffon.com)
Love the so completely unexpected pairing of purple with bright orange, and then the denim and leopard print heels. (morepiecesofme.com)