Good point, but OP's point is that they can't hide behind demos. Anyone who requests the source will most likely get it and be able to see what's going on.

Indeed, that part is accurate. It would be technically interesting if the tech demo was a part of UE5 source release. I'm not familiar if they've done that in the past.

Demos are sometimes released in the Unreal Marketplace. Unity often does the same in their own store.