You can't collide with 'falling pieces', you don't get damage from them, these are just animations. But if you collide with a still existing plane itself - the thing that still has an icon attached to it, you will get a collision & damage.
When you watch the film provided, you see that the enemy was still alive on your frontend, the icon was still showing. This thing can indeed happen during head on kills/collisions with their high closure rates - the kill message text arrived a spilt second before your front end realized the enemy is gone, but that's exactly when the collision happened.
