Yeah, this is kinda fucking stupid of Jon. You fought with wildlings, even some Whitewalkers, but your super-sensitive direwolves growls and you ignore him. You really know nothing, Jon Snow...
It was already established that wargs can't stand each other. Even Jon has an instinctual dislike of the wildling warg. So I find it understandable that he would dismiss Ghost's reaction as being caused by the other warg, rather than some sort of danger warning.