Was this sexual assault?

Edit: Thanks to everybody who offered advice! I'm basically over this whole thing at this point and wanted to give a little update for anybody who might stumble upon this later. Ultimately, I think this definitely qualifies as sexual assault. I knew this before I made the post, though. I didn't want it to be true at first, but I've since decided that it doesn't matter what it's called. At the end of the day, it was just an unpleasant experience that I want to avoid going forward. Having the "sexual assault" label (or not) is not that big of a deal.

My main concern was about STIs more than anything. I wasn't able to get tested on the ship. And I couldn't get PEP from the pharmacy onshore because apparently, it's a prescription drug in that country. I got tested as soon as I was back home. Everything was looking good. I've started hooking up again and I've been having a good time as usual. But this taught me a very important lesson about being more assertive and careful when meeting up with strangers. You live and you learn!

Original Post: I'm (23M) on a cruise and I just hooked up with a random dude on deck (35M). It's not a gay cruise or anything. It was early morning and we met up in the bathroom after "talking" on grindr. We didn't discuss what we would do. It was fun until he tried to get me to top, which under normal circumstances would have been great. But he was clearly not prepped and we didn't have condoms. I didn't want a) shit on my dick and b) STDs. He seemed fine at first.

Then he gestured for me to sit on the closed toilet. I thought he was going to give me a bj but he turned his back towards me. I said no again but he said he was only teasing and wasn't going to do anything. But he all of a sudden slid my dick into his asshole without warning and was riding me. I was already really close at this point. I tried to hold him back but I was on the edge and the pure physical stimulation made me cum inside him. He was delighted but wouldn't stop even though I was trying to not let him ride me anymore. He came soon after (thankfully) and got up.

I never felt so disgusted. I definitely got shit on my dick, and hands while I was cleaning up. I still feel incredibly dirty right now even though I just took a shower. He wasn't even that attractive, I was just horny in the morning and made a bad decision. I feel dirty not just because of feces and potential STDs, but also because things felt sexual assault-y. I didn't want to do something and clearly communicated that, but he proceeded anyway.

Am I overthinking it, or would you consider this sexual assault or something? What do I do? How do I get over it? I'd appreciate some perspective. This is the first time something like that has happened to me and I don't know what to feel.