His "secret" is basically sanding. Lots and lots of sanding.
https://www.amazon.com/Open-Circuits-Beauty-Electronic-Compo...
Still doesn't change the fact that this is an untested board design that relies on a difficult-to-source obsolete chip.
If some pins are swapped by mistake e.g. power and ground you are screwed.
Caveat emptor — unfortunately this was buried in the description.
At this stage in a project like this, I’d expect the people who were getting boards fabbed to also have the skills to sanity check the schematics and layout before they sent the gerbers off to China.