I can just imagine Wrench's excitement at having someone taking interest in the kinds of things he's good at, only then to be stricken with this moment of realization like, "Am I indoctrinating a kid?"

No it's fine. This is totally fine and normal. And Wrench would be super pumped about learning how to use a boomerang in exchange. He's pretty good with ranged weapons, but that's one he's absolutely never encountered before!