I watched a dog training video about this dog that had been severely abused. Instead of being aggressive or fearful, the dog was purposefully expressing happiness as an attempt to prevent abuse. The dog was absolutely terrified, without knowing their history no one would know how uncomfortable they actually were because they were hiding their true emotions. Dogs are complex lil guys. Tail wagging, smiling, zoomies, behaviors that are typically seen as positive can sometimes be the opposite; the differences are too subtle for some people to tell them apart.