This is more to do with game dev tools that are relatively cheap these days.
He didnt make the models from scratch because he likely used RealityCapture and all those photos to "scan" the environments.
Something like substance or mixer will also quickly turn photos into textures, so authoring textures becomes a breeze.
Quixel Megascans also end up shortening dev time because they have models and texture for pretty much everything someone might find in the real world, that team is constantly out in the world scanning stuff and you can remix it to fit your enivornment.
Unreals Nanite means the user also doesnt have to worry about LODs or even optimizing models so he can just inject those million poly models into Unreal.
Realtime Global illumination means he doesnt have to worry about baking any lighting data so its plug and play effectively.
Inertial Capture Systems arent very accurate but are pretty cheap so you can get the mocap done quite quickly.
Epics MetaHumans means making human models is pocket change now, where before human models were some of the hardest things to make
(Might be personal opinion because im a hard surface modeller and doing any sort of sculpting fucks me up)
Unfortunately most of this doesnt really work if you are actually making a game with any soul, cuz real life isnt actually anywhere near as interesting as people think it is.
The environment is graphically amazing sure, buts its more rocks and shit he found while out on his walk.
The demo has near no art direction.
Most of these techniques when skipping the actual game dev work dont help much if you are making say a stylized game, photoreal textures will look out of place.
EDIT: Looks like I was on the money with most of what I assumed he was using.
Unreal Engine - Obviously
Quixel - For textures and other models
Rokoko - For motion Capture
Motion Builder - To "fix" MoCap
RealityCapture - To turn photos into 3D models
PBRMax - For other textures and models
EDIT2:
Yes I do agree with OP that these tools make game dev alot easier and faster, certainly should reduce the budget needed to create "AAA looking" games.
Theres even sound repositories now so needing a dedicated composer is less of an issue for a indie developer.