Why do guys rub a girls thighs and touch their hips?

I don't really have a big butt either, but I am skinny and have nice legs and hips and stuff. Anyways, I remembered about two months ago I hung out with my crush who's also my best friend (we both like each other though because we've said it lol). He put his hands on my thigh when we were sitting and I don't know if he really rubbed it but I think he went up and down a few times. It was kind of a tight grip I guess you could say it was a tight grip. He'd also put his arms around my hips and stuff a few times, like when we were hanging out I'd walk by and he'd reach his arms out and touch them. I know it means he likes me because like I said, we've told each other. Then today I see my friend getting her thigh touched by her boyfriend just like my crush did to me. Why do guys do it? I'm so confused! Lol