Sexuality and early puberty

So at times my nine and a half year old son will take my phone, watch kids Netflix on it or watch kid type videos (spiders fighting snakes etc) on YouTube. Up until this point Id always tell him not to watch anything not for kids and we have never had issues. So my fiancé gets on my phone to look up a music video through YouTube history he watched yesterday (his phone is dead) and asks me what I was watching on YouTube. I said nothing why? Well in the history it went from snake fights to women undressing videos 0_0. Im instantly mortified realizing my almost ten year old son has somehow fell upon this and was watching these videos. So he had a talk with him and my son admitted to touching himself because it felt good etc but that it was the first time he had ever seen anything like that and it was an accident. His dad proceeds to tell him that although he is not aloud to watch things like that because he is too young and it's not meant for him, that masterbation is normal and technically a healthy part of growing up. That it shouldn't be done anywhere NOT private etc but that he doesn't have to be ashamed of it.  My son thanked him and told him he thought he had a problem or something was wrong with him because he did that. So... As extremely uncomfortable as this was for me to hear back from his father about... It's important that kids are comfortable with their sexuality. At some point things at certain levels need talked about and I don't want my son to think he's abnormal for masterbation. I did research and it has shown that kids younger then him (as many of you know) touch themselves constantly. It's not abnormal for children to do these things. Especially since he already needs to wear deodorant and seems to be growing up faster than Id like. Just wanted to share this extremely uncomfortable topic lol for future first time parents and those ️maybe going through the same as I am. Sigh. 😳