Played island hardcore, unlocked 2 trucks normally, driving near them. However when I uncovered a watch point 2 trucks in that watch point became uncovered AND unlocked, I basically could drive them even tho they were very far and never been near there before.
They were 2 255 with medium log carts (trailer and cart, ready to pack) and spare wheels, next to a lumber mill, and they both were close to each other.
Not sure if its a bug but if it isnt an explanation would be good.
Edit: happened again in the 3rd map I played, coast in hardcore too. 2 trucks unlocked by uncovering the watch point. Probably happened in the first but I didnt notice.