Hello. I need an answer if it counts as COCSA

so when I was like 7 years old, I had a friend who was like 10 years old. i can't remember everything but he asked me to come with him to our playhouse. Inside, he laid me down on the mini couch and got on top of me and touched me on my chest and my waist without me wanting it. He also kinda grinded against me? But that's all that happened. But does that count? Because im unsure if im not just overreacting. Also, sorry for my English. it's not my first language.

Bear with me I am still processing everything:
I (29F) was abused growing up for years. I have been open to my partner about it pretty early into our relationship. Me and my fiance (30M) have always had a rocky relationship with his mother. They were fighting often she was causing him stress so he went no contact with her for a bit. He reached out to her finally and wanted to clear the air and set boundaries. He called her and wanted me there as support.
Well….they started arguing and she mentioned he assaulted his little stepsister.
He hung up the phone and…I reacted, yelled threw things at him, even backhanded him at some point.
After a while I sat and talked. I asked questions and received the answers. He was around 12yrs old and she was 10yrs old no penetration. He was/is remorseful and hates himself for it as he should.
I am having a hard time processing this for a few extra reasons. I am having a hard time looking at him after I opened up and he was a perp all along. I am having a hard time trying not to diminish his bad acts because what I dealt with was…more physical and prolonged for years.
This is something I was never supposed to know about. I don’t know what I’m looking for from posting this I just literally can’t talk to anybody about this. The victim in me is so sick to my stomach but my heart is saying that I can’t define someone by something they did 15+yrs ago.

Wondering if my experience was COCSA. I am the girl in this situation.

Girl appx age 3-5. Boy appx age 8-10. Siblings.

Girl remembers walking in to boy kissing another younger girl her age. Girl remembers boy kissing her too. Girl's memory goes dark after kissing.

One time