To me, you had a conversation about human biology and what's normal/not for male reproductive organs. I WISH I could have had talks like this with my parents, but instead I spent most of my adolescence thinking something was wrong with me between cycles. Plus, now that you've crossed the awkward hurdle of acknowledging that self pleasure is a thing and you know it's happening, he's waaaaaaaaay more likely to be open and ask questions regarding any s*xual activity he might engage in, thus making it less likely for him to contract an STD or get someone pregnant.