Please someone explain!

Cast iron is “seasoned” to make it nonstick. That means many layers of oil build up as a sort of polymer. The point is to keep it “dirty” in this way. Cleaning it down to bare metal means she’d be forced to re-season it, which can take considerable time/effort depending on frequency of use.

Isn’t the “seasoning” PFAS?

No, that’s the opposite

You can season nearly anything with oil. Except aluminum, which needs a Teflon coating or it gets nasty very fast. Except Teflon is non reactive to nearly everything

Except pfas. You can dissolve Teflon in pfas and spray it onto aluminum

? Teflon is a PFAS