It is not unusual for people to erroneously think that if they do anything nice while interacting with a dog who is behaving fearfully that they will be reinforcing the dog’s fear. This includes being unwilling to provide the dog with any social comfort, treats or gentle words.
While we could reinforce a dog’s fear by doing something that would startle or scare them when they are afraid, shouting RUN IT’S GOING TO KILL YOU! for example, being kind, gentle or supportive is not going to have the same effect. We are not telling a dog they are right to be afraid when we hand them a treat or try to comfort them. Emotions don’t respond the same way as behavior does when something good is presented in their presence. We know this already. When we kiss boo-boos on the knees of crying children we are not expecting to make them cry more or become more upset.
Comforting a fearful dog is not going to reinforce their fear, but it may not help them if they are very scared. If they do not seem less fearful when we provide comfort we should consider that what we are doing is not providing actual comfort to the dog and we need to do something else. Removing the source of the fear or removing the dog from the situation are good places to start. This article by Dr. Patricia McConnell addresses the myth of reinforcing fear.