Yes, ghost pedalling. The pedals don't just spin on their own, it is because the cranks and chain don't have enough friction holding them in place. Remove the spacer inside sealed cranks, slightly overtighten the cranks (very slightly) and keep your chain tight - your cranks will never move. Doesn't matter if you have a freewheel, cassette, or freecoaster. The cranks will stay where you leave them.

Can make crankflips tougher though.