I own and run a metal shop, and those rust specks are precisely steel dust that settles on stainless, starts to rust and etches into stainless. Causes are generally grinding/sawing mild steel near stainless, and metal brake dust. Either way, stainless is hard to upkeep, thats why many stainless appliances have clear coat applied. Its a good idea to apply clear paint protection film to the Cybertruck to keep contaminants out. I'm surprised they haven't applied a clear coat to it from the factory.
To be fair, there are maintenance concerns with traditionally painted cars, especially dark colors, and even more so with matte colors that are becoming popular. When it comes to wraps, there are separate concerns as well.
Having said that, I did a quick search on the stainless alloy used on the Cybertruck, and all i see is 30X, which is likely 304. This is not what I would use for exterior applications, I'd always use the more expensive 316 alloy.