I can't tell. The first bang sounds exactly like the third bang from an adjacent firing point. I can't see the trigger finger or anything else move. The only person who would know was the OP who would have felt the striker fall, followed by the bang.
The gun dropping looks like typical heeling, where the hand tries to fight recoil by pushing the gun down. It tends to start just before the shot goes off, causing low impacts. The target certainly has those strung vertically, which is the result heeling causes, so it's probably something the OP would benefit from working on eliminating by focusing on follow-through. But whether it got going mostly before or after trigger press in this case, without seeing the trigger finger, I can't tell.
If the gun was new and never stripped and cleaned, old lube certainly could cause a light primer strike which certainly could lead to a hang fire. It's not high probability, but it's within the realm of the possible. The fact the shot fired and ejected normally suggests the powder was working OK. Contaminated powder usually produces a weak shot, but I suppose it's also not beyond the realm of possibility for a minority contaminated portion that happens to be over the flash hole to delay ignition of the rest. Again, just not very likely.
I would tumble cases in dry corncob (or in a solvent I allowed to dry off completely) after sizing and before continuing the loading process if I were lubing the cases inside and out.
