Maybe, and likely, given all the other cuts they made, but as far as I know it's not actually known, which is frustrating. That said the article calls it an SUV and isn't exactly riddles with facts, so.

The pictures from the cybertruckowners forum show something on the surface causing discoloration, like road grime or dust disintegrating in the rain, not like rust forming on metal. I've restored a few rusty stainless kitchen knives in my day, absolutely abused ones, and even cheap stainless doesn't rust like that, that fast. I'd expect rust pin spots that bad on a chipped paint job over mild steel, on stainless that's had iron embedded in it (like from scrubbing a sink with steel wool, or on chemically altered steel (like filling a stainless sink with bleach and putting an iron pan in the same sink for a while).

All we need is somebody to drive by a pressure vessel fabrication shop and get the panels zapped by a PMI gun. We'd know instantly.