Yes, Johnny Gargano was the one responsible for hitting Alesiter Black from behind, putting him on the shelf, and costing him his chance to regain the NXT Championship.
A brief clip of Gargano jumping Black in the ring was leaked from the recent round of NXT TV tapings, but it wasn't explicitly clear that he had been named as The Dutch Destroyer's assailant until tonight.
After the episode, NXT aired exclusive footage of an interviewer attempting to get some answers from Johnny Wrestling, but it doesn't look like the former fan-favorite is ready to spill just yet.