Invalid comparison Xaus was never off the ground long enough. His was 1 long multi year crash in perpetuity
Depends on your definition... If you put it on a scale, I think it would be the same, because the helicopter is still exerting it's force through the air downwards onto the floor of the truck?
If the train accelerates to a static speed, on a straight track and no air is flowing through the cabin, and then the helicopter takes off, the helicopter will fly the same as it would in a normal stationary room. If the train accelerates in any way (turns, or changes speed) the helicopter will move w.r.t. the cabin.
Only if the operator is in the truck with it which then invalidates the experiment per the original meme here.