Actually, there could be many reasons for a ladies approach.
It could be a friends place being borrowed and why would your friend have gentleman callers coming to see your friend, where as two people coming together, is just that two people visiting the persons place.
It could be a last minute jerk, it's your way out, the ladies way out, just drive fast man, drive very very fast..... I've also had people pick me up at home for an outcall!
It could be the ten minutes you need together to just get that uncomfortable jitters out of the way, so that when behind closed doors, there's no need for introductions or ice breakers.
It could also be that, if you were a bad guy, and your going to walk up to my door with a shot gun, and ten friends. I'll see them in your back seat when we meet up....security maybe.
Who knows though, woman have the ability to change their course of direction on the head of a pin and its up to you the man not to lose pace.