They aren't dumb. They are professionals who do this sort of thing for a living.
That said, most companies don't etch their own boards. That part of the build process could be skipped by sending your schematic out to one of the boutique board fabrication places. They aren't terribly expensive and it avoids having to deal with nasty chemicals. The article even mentions this and I would highly encourage it myself, at least until you have a few boards under your belt and are feeling more comfortable with diving deeper into the process.
Assembly carries a different set of risks from powering something up. But as the sibling comment says, the assemblers are skilled technicians. They might lack theoretical background but they will have had a lot of apprenticeship.
The EGS002 looks like a really neat subassembly. It's just that at 1kW the safety issues are significant.
That said, most companies don't etch their own boards. That part of the build process could be skipped by sending your schematic out to one of the boutique board fabrication places. They aren't terribly expensive and it avoids having to deal with nasty chemicals. The article even mentions this and I would highly encourage it myself, at least until you have a few boards under your belt and are feeling more comfortable with diving deeper into the process.