Was this sexual assault?

I don’t remember how old I was when this happened, maybe 9 or 10? I slept over at my best friends house and was coming back upstairs from getting water at 11pm. My best friend called me from her step uncles room (he was two years older than me) and I thought they were just trying to scare me so I went in. It was pitch black and she kept calling me until I made it over to his bed. He grabbed me, placed me on top of him, and began grinding up against me. I told him to stop and to let me down but he said he wouldn’t until I kissed him. I didn’t want to, but I really wanted him to stop so I did.

Was that sexual assault?

Edit: thank you guys for letting me know. He got caught for sexually assaulting that best friend of mine but no one ever knew what he had done to me. I also have a hard time saying it’s sexual assault because I was sexually assaulted by a different guy a few years later and it was way worse than that first time. I didn’t think it was because it wasn’t as bad as the second time but I was wrong.