A lot of it is the baked lighting (he mentions it takes about 7 hours to bake the lighting if he wants to change the scene! https://www.twitch.tv/videos/1144467679?t=00h18m03s).

I love doing 3D stuff for fun - but like you, everything looks like minecraft blocks from different worlds. Certainly not real.

But if you open Blender and put a couple of cubes in a scene and render it using Cycles (in the Scene tab change the Render Engine dropdown from the default Eevee) then the cubes looks way better: https://imgur.com/a/q9xvZeI

The ambient occlusion, and proper light bouncing and reflections make even the boring-est cubes look pretty good!