I just bought a cast iron pan

Did you see the pan that he cooked it in? Butter still not melted, he probably didn't preheat at all.

That explains it, fucking leaf.

i read you should season it at 500 F
the point is you want it to be higher than the smoke point of the oil you use, science stuff molecules bonding, better seasoning
i think it was serious eats i read it, not sure