Don’t say it’s an overthought, it’s just a joke, but by the way he said that “hello” just shows how uninterested he is in what John was trying to teach him about herding cows. But his interest in killing and handling guns really comes out when John takes him hunting. Jack initially doesn’t want to go and rather stay at home reading his books but when John insists him to come he becomes excited with the guns and killing animals. He even gets overeager to hunt a bear but ultimately past the price for his inexperience when John has to go rescue him. But this small detail that I’ve seen actually go unnoticed is a major hint at Jack becoming something like John if not worse, later in the next few years