They specified they’ll only assemble the machine in US. You barely need a bunch of people with screwdriver for that
That's most definitely not what they announced. Specifically in their announcement, they said some manufacturing will be moving stateside, and they listed the locations involved in part sourcing. They also specifically said manufactured in US, not assembled.
According to government records, the Mac Pro only ended up getting an import exemption for 10-15 "parts." Obviously the Mac Pro has more than 10-15 parts, and those 10-15 parts are likely including different BTO options. The paperwork stated that options like the video cards fall under those 10-15 parts.
I think Apple is double dipping a bit. They're counting Oregon as a "source" when that is likely the Xeon CPUs. But there are other locations they listed that are likely new sourcing.