My dad used to put small holes in my sisters walls to spy on her

My dad built my sisters room in the basement when I was like 9. She’s 4 years older than me. When he was done building it, he showed me little peep holes he made in the corners of the walls. He made it sound like it was a top secret fun thing, that we were “spies” and we needed to do this to keep an eye on her. He said it had to be a secret and I couldn’t tell anyone. My sister was pretty sneaky and misbehaved a lot, so to me at 9 years old it made a lot of sense. When my sister had friends over to spend the night, my dad and I would go look through the peep holes to make sure “they weren’t doing anything bad”. At almost 30 years old, I suddenly remembered all of this and just how WEIRD it truly was and it makes me question everything. What IF he was spying on her after she took a shower and was changing? I never told my mom about this and I don’t know if I ever will, I’ve never told anyone at all. This was WEIRD right?? I almost cannot believe that was real.