In my view it's a simple 'hit and run' traffic incident, whether or not it involves cars.

I'd report it to the police. A vehicle rear-ended you (by definition always the error of the vehicle behind you) and then ran off before exchange of addresses. Unlikely the police will take action against the rider but at least it would establish a formal paper-trail. Might come in handy if it becomes an insurance issue.

Plain and simple 'hit and run' traffic offense. Just because 99.9% of 'standard' hit and runs involve cars doesn't mean the same traffic codes don't apply to bicycles too.

(Slaps forehead ! I *was* rear-ended on bike once by another bike, by the neighbour's kid of all people, in a terrible storm. Couldn't see 2 m ahead of you. I was 13 at the time and knew too little about these matters to ask for his address if he'd been a stranger. The fact that it was the neighbour kid meant the insurance problems could be worked out quickly).