From memory, I believe PSU was penalized on the play. PSU had lined up with 10 on the field and the missing PSU player realized it late.
Reviewing the video, I see 10 PSU players and 11 PU players are visible being lined up. At 17:50 of the video right at the snap you see the foot of the player (#19 Anthony King) who made the tackle moving around the 49 yard line sideline towards the line of scrimmage. He ends up making the tackle.
I think it is in the referees discretion as to whether a TD could be assessed. I’d imagine a combo of the above along with Brandon Short (#43) closing in, a penalty was deemed appropriate.