If you are going to be that picky all materials have creep and flow, the real question becomes how much and how fast. Additional all material compress under load, with some rebound, again something that is important. We won't even get into the thermal expansion/contraction differentials in a machine and materials used.
Its not being picky, its about understanding the accuracy a machine tool requires, the techniques and challenges in bringing it about and being able to observe the absence of said techniques.
How accurate, as in specifically what tolerance for flatness, would you have to have in a machine you made to claim it was at all comparable to a commercial cnc mill? Then, what techniques did you see in that video that makes you think they might have achieved that tolerance?
So can they produce an accurate machine, easier than lets say 30 years ago.
Why do you say that, epoxy granite? It's been around for awhile however EG doesn't make achieving accuracy any easier; it makes it possible to make a fabricated machine with better than cast iron vibration damping properties.
The only question becomes are you smart enough?
I don't think smart enters into it. its a matter of knowledge. I have reconditioned machine tools. Its not rocket science, but it does teache one how to create accuracy and the challenges in doing so. So yes I think I have the knowledge. As for smarts, I'm smart enough not to bother when there are paths to a far superior machine for less effort/money. To each their own of course. The point of my posting, as I said, is to discussion machine tool accuracy, what's needed, how you achieve it, whats missing in the video, etc.
I don't question that they are smart enough but they lack knowledge on how to create accuracy, specifically in the realm of flatness. A rather critical part of making a machine tool. Or at least if they have it they're keeping quiet about it.