I would suspect that the horse has a latent tendency to crib, and stress will bring it out. I have seen cribbers stop cribbing when moved to a new barn until they got the routine figured out, and I would imagine that your horse is the reverse of this.
Also, some horse's object to having their turn out time reduced.
Some riders change their horse, they change their saddle, they change their teacher; they never change themselves.
Remember the horse does all the work, we just sit there and look pretty.
I've had my horse since he was 3 1/2. Until age 6, he never cribbed a day in his life (including a 6 month period of stall rest for an injury). During his six year old year, I had him at a terrible barn for several months (they stopped turning out in winter, and there were other major stressors there). He began cribbing as a six year old. It was severe, up to ten times in a two minute period, for example. I moved him to another barn (he was still six at the time), and the behavior stopped. He will be eight in May, and he does not crib. The one exception is that he will crib on the crosstie if he is crosstied. I have never seen him crib in his stall at this barn, and neither has anyone else. He also does not crib outside.
Knocking on wood!!!
Hopefully your horse was removed from the stressful situation quickly enough that he will let go of the cribbing behavior quickly.