Well, yes I suppose compared to how some reference them I do. However I've heard both be described as the other many times.
Personally, it makes more sense for the change that modifying the shock length does to be called droop. I picture it in terms of the TC. You raise the chassis until the tires leave the ground and this is what you call droop. So for a pan car you would lift at the spring until it stops (or until the tires leave the ground), so that would also be droop to me.
The amount the rear pod "drops" when you hold the car up would be the sag.
I guess it all depends on how you look at it, but the theory is still the same.
Cheers