A guy patted my thigh?

Basically, I just met this guy today at a casual barbecue. I'm a first year, he's a fourth year (I'm 18 and he's 20). When we met, we chatted, found out that we had two mutual friends, and we talked for four hours total. When it was dark, we were sitting by the fire pit - keep in mind that all day we've stood fairly close to each other, but I didn't think anything of it, and he rested his bent arm on the back of my chair, still didn't think anything of it.

Then, at one point, he says, "I'm going to the bathroom" and puts his hand on my thigh, like a reassuring placement and then goes up to go to the bathroom.

When he comes back we keep talking, and when I leave there was no mentioning of exchanging numbers, and he gave me and the the other girls hugs goodbye.

Was that casual?