You have answered this problem yourself. The flop could easily have been an orphan but A passive player who folds to most Cbets calls yor pot size bet. I dont know what he had but it beat your nothing on the flop. Looking at the flop anyone with a piece of it also beats your jacks. check fold.
I am interested in your pre flop raise, SB 6BB with AJs. Its not in my playbook the max i would have gone is $8 and to be honest it would have been a marginal play for me most times i would have folded this pre flop.