After the boys checked into a motel to take a break from all the driving, Jack started playing with the TV, and he discovered an episode of Scooby-Doo.
He was clearly interested in the show, but Dean switched off the TV before Jack could see much of it.
Now that he’s seen Scooby-Doo and shown interest in Scooby-Doo, doesn’t it stand to reason that the Scooby-Doo crossover will happen when Jack somehow uses his abilities to zap the boys and (somehow) Castiel into animation?
Even Jack was discovering abilities that he didn’t know he had.