Basically he lands a deep j.b then he double jumps and hits j.a then D for the persona follow up then he can come down again with j.b for a combo. What happens is the opponent switches to crouch block after blocking the j.b (expecting you to land and go low) you jump again for the instant j.a. Since they are now crouch blocking they get hit by an over head j.a but normally this wouldn't land in normal circumstances and that's all do because their hit box is still standing in this event.