Yes, on a mature seasoning layer. A quick twenty-minute sauce is harmless; simmering acidic liquids for four hours will slowly leach metallic taste into the food.

You left too much oil on the surface. Excess liquid fat pools and partially oxidizes into gummy resin instead of forming a microscopic, fully cured film.

Scrub the rust away with steel wool, dry the iron over immediate heat, and wipe a microscopic drop of neutral oil over the bare spot.