if he’s usually a charismatic person, it could mean nothing, but if he’s really shy, it probably took a lot of courage for him to touch you. shy people have a very different sense of space.
It all depends on the situation and the extent of their relations. Look for other cues, such as other body language hints, to show if it was a friendly gesture or more than that.
As a guy, I would give a quick back scratch, or light rub, to a female buddy if I feel friendly at a particular moment. It wouldn’t be often or extended though.
Did you ask him? Can you ask him? I’d ask him, gently and with a smile, of course, the next time he does it. “So you’re a masseur now?” Or something like that.
could be he’s testing the waters to see what where to rub next. Friends and or business partners should not invade your space. In some situations that’s sexual harassment. Mr touchy should keep his hands in his pockets, and concentrate his speaking skills, untill you give him the ok
To explore your backside. I think it was very forward of him to do and he was testing your ability to shut that type of activity down. Unless it’s friends with benefits. Good luck.