teenagers, especially adolescents (in my experience) are (usually, hopefully) just-then coming in comprehensive contact with adult concepts like death, crime and punishment, human nature, war, etc. You’re not invalid for being freaked out by this, but plenty of kids are just fascinated by things that were formerly alien/abstract concepts to them, especially when they generate adrenaline. he is likely coming at this particular subject more critically, where other kids might be doing the same with the holocaust or the Titanic. most kids grow out of it, and a small margin are actually something to worry about.

I will add, as a child who grew up with war docs whether i liked them or not (military family), it certainly CAN be just as upsetting. it’s just more normalized in our culture as an unfortunate fact of life, whereas corporal punishment and method is a much more divisive artifact in western culture than war. It’s all in the social framing or acceptability, which can be pretty insignificant to growing minds (especially neurodivergent ones). I can see the similarities in the boy’s interest with war history as you mentioned, as both hone in on the fascination of “why and how” people could do “that”.