Think about the graphics we got with a 970 running full blast at around 40fps. It wasn't close to this. Yet, that could run on a 970 in-engine ... because in-engine means nothing anymore.
"ACTUAL GAMEPLAY FOOTAGE" or bust.
There was a comment by the creator of that scene where he said "it's easy to make things like that in UE4 with no game code". I've been trying to find it but I can't right now.
This was it:
its easy to render in real time, when you have only little part of scene and no have any AI or somthing else hard calculations