There really isn't much of any prefabricating done. I would say roof trusses were the only thing done in advance and that is normal for any buidling project. The quick-builds I've worked on were all done on site. The groundwork did take months to do though.
I would think you could swing by a likely site anytime you like and take zillions of photos. There really isn't anything for them to hide. The only time we had round the clock people there was the week before the "quick build" actually occured, and then only to keep an eye on the materials.
Now I'll mention this. I was in a construction union for 32 years. I'm a house painter by trade. So when our unions wanted to put up a house fast we did it honestly. We poured foundations and had the front door painted and locked in less than 14 hours. The family moved into it that evening with some wet paint still there. Now the record is closer to half of that time.
So the quick builds aren't all that quick and they aren't just a JW thing either. I enjoyed working on most of them except for a few idiots that actually thought they knew something about construction.