Some people consider nudity of the child being beaten to still be sexual abuse. For some,it doesn't have to be full nudity, exposing the buttocks is enough. The abuser doesn't have to be undressed too.

This link says coerced nudity is sexual abuse. I'm guessing you had to strip for those beatings. Which would make it coercive nudity.
https://www.dshs.wa.gov/altsa/home-a...nd-signs-abuse