It doesn't automatically mean he wants to date her, but it's a good start. he's being friendly and open.
I wouldn't necessarily say that. It depends on a person's personal bubble. Some are more touchy with either gender. Personally, I like touching the sides of women I like. Sometimes the small of the back if approaching from the side.
I wouldn't say it turns me on though. It is just a nice gesture that says I care about you. If a woman touches me, I wouldn't assume she liked me or was into me.
One time I rubbed my boner on my friends leg in a non-sexual way.