Nice video mate.
I think this video was shot at Shoei factory. Amazing how the guy ass/disemble FG42 in a quick manner.
Another convincing scene to buy this...

shaz,

I think it is Shoei factory, too. In the background you can see some machines, there is also machine noise in the background. I got the link in a Shoei "newsletter" sent by Tomio - he wrote that the video was done by his friend. (this gets me wondering if the person would be Tomio himself?)

As for (dis)assembly speed - I was just as amazed as you! I imagine you get it from working extensively with replica, either designing/trying/testing or just handbuilding this replica. Excellent dexterity!
I wonder if this way is closer to the way soldiers did it during WWII. According to FG42 manuals soldiers were not allowed to do complete stripping, only cleaning and some basic maintenance. Only gunsmiths were allowed to go all the way.

One "shocking" thing here is that when I disassemble something, I do it very slowly and delicately to avoid scratches or accidental damage due to mishandling. It is very lucky when you are in position to strip/rebuild quickly without worrying about anything like the person in video :-)