The forum posts contain images

https://www.cybertruckownersclub.com/forum/threads/rust-spots-corrosion-is-the-norm.11988/page-2

It looks like surface contamination to me, which can happen when iron or non-stainless steel gets embedded into the surface of the stainless through abrasive action, like scrubbing a stainless sink with steel wool, or as some people have stipulated, iron dust from the rail carriers during transport.