Is It A Rear Engine Or Rear Drive That Makes It A Pusher?

It is more a description of the chassis configuration than the driven wheels. If the engine is in the back, it's a pusher. I may well be wrong, but I think the term comes to RVs from transit bus descriptions (and may well have been influenced by aircraft configurations with pusher vs. tractor propellers).

I suppose it would be possible, though not particularly sensible, to have a front wheel drive pusher chassis.