A sweep has to be initiated from some sort of guard so:
I have guard, they start to pass, I turtle to defend and push them over geting top position (even in their guard)... that ends up being a sweep.
On the other hand I'm in bottom side control. I roll them over and end up top side control. No points for a sweep there.
Seems kinda wrong that in the first situation I get points even though I'm defending in the course of the sweep and may end up in guard, where as in the second case I would end up in a much more advantagious position. Just the way it is though.