[Lupa is trying to teach, by explaining what he's doing and why, at least. He's just never had to instruct someone that didn't have basic competency with firearms literally programmed into them before and it's really showing.

When Mando speaks to him Lupa does pause his lesson for a moment.]

I was Leader of my Tribe.

[He also doesn't seem to realize that that's probably not sufficient explanation/answer to the comment about his expertise.]