I expect that the floor of the bin is elastic in the technical sense - it returns to its resting form when no force is applied. When the BANG goes off the base of the bin is compressed into the floor, hard. This lowers its center of gravity. Then it returns to its previous shape, the CoG rising as it does so. Once it has returned to its original position it discovers, rather to its surprise, that it's now travelling upwards, and so it continues to do so.