Mmmm, my dad was a veterinarian and me being a dog trainer ( well, for 4 dogs of our own where I learned a lot from where I trained my dogs), so i got to a lot of my dad's clients to help out with their new/adopted dogs that behave frightened.
It's weird that your dog still has the same behavior after one year with "his own family".
I think playing with a dog has a lot of "accidental" touches that should make him accessible to those actions.
I also don't think it was a stick, since my own abused dog was afraid of sticks in particular. As long as we had one it was okay and he didn't care ( since we played with it). But if someone unfamiliar would try that, he would become aggressive ( happened one time many years after, when an older guy with a walking stick came over and wanted to silence/move the dog with his cane. Luckily I was nearby and heard the sound immediately )