Yeah. My understanding is that Deloreans were shockingly rust resistant but were also panels specifically so that they could be replaced.
I don't know metallurgy/material science well enough to know if cybertrucks actually used good quality stainless steel or cut corners. And I can easily see a world where people assume the dirt is rust because of paranoia or just looking for internet drama/clout.
But... Rust or no rust, those cars are pretty fucked. Because they don't even have a clearcoat. And considering we are in the season where roads are covered with salt and sand and cars are constantly bombarded with a highly abrasive slurry at speed, those panels are going to see a LOT of wear and damage.