First use after seasoning- what did I do wrong?

So I got a new ( pre seasoned ) cast iron and I proceeded to season it three times before my first use. I seasoned with food grade oil and putting in oven for an hour and repeated 3 times. I used it today for the first time to make egg fried rice( no vinegar or sauces were added or even tomatoes or lemon) . I left the pan with food for 1 hour or so before emptying it and washing it with plastic brush very gently just to clean it, I did not scrub hard. After drying up on the hot plate before oiling it I could see blotches that seemed like rust.

What the f did I do wrong? For the time being I just oiled it and kept back. Do I have to season and do the entire process again? Or do I continue using it? Rust is pretty poisonous isn’t it? The fried rice has some burnt bits that tastes metallic too

Makes me wanna go back to my Teflon 😭