I don’t know so you decide for me

I used to share a bed with my sister. In the winter one night, she draped her leg around me and started humping me. She had thought I was asleep. I moved a little so she’d think I was waking up. She immediately stopped and casually removed her leg. I was 9 at the time and she was 17. What is that? Is that sexual assault? We both only slept with a shirt and underwear on. The thought of it really makes me uncomfortable and I’ve never told anyone this. It’s been 9 years.