Passive to me, means that when body is the leader and the hand and arm follows, where as active arm swing, body reacts to hand/arm motion. Dog waggles the tail image worked well for me when I was a body swingers/turner. When my shot pattern became bigger fade/slice, I ended up seeing McLean which agreed that too much body can be a very bad thing and gave me "L-to-L" drill. From there ended up seeing Bender who is also CF arm teacher. Transition wasn't fun at all.
I get what you are saying here, and I think a lot of people define "passive" arms exactly the same way. Its why I put passive in quotes in my post earlier, as the arms are full of muscles and can never truly be passive, not like a rope or anything. They just feel that way. Maybe a better word for describing the feeling is secondary, as in, firing the hips is primary, and the arms are secondary in the swing?
Somebody correct me if I'm wrong, but I always thought the drop of the arms was a result of anatomy as opposed to gravity? The hips and shoulders are connected in such a way that when you tilt the hips in one direction, your shoulders generally follow. Therefore, when you start your downswing with your hips and you press your weight forward, you shift your left hip up and your right hip down, which causes your right shoulder to tilt down and drop your arms. So yes, you're not using your arms actively to drop them, but it's not really gravity either.