Which may have been tailored for the demo - for example, put a very small battery pack in there, so that the weight is much lower than the weight of the actual car would be - it only needs to drive a few meters, doesn't it?

Based on the record of Musk & co straight out LYING in such events (remember Solarcity?), I am very confident in saying that a large portion of what they demonstrated they have not actually solved how to fit in a real production car.

There is no amount of evidence that will ever change the minds of some of these posters.

They could be in the unit when its happening and there would still be some counterclaim.