In the case you brought -the guy just wants to warm up Stam a pot
RM”A says the pots which very much sounds like that’s their Shabbos food (certainly their only hot food, which is considered a tzorech gadol).
The Biur Halacha (probably the one you were referring to) is explicitly only mattir (and hesitates to do so) where there’s no eitzah, and only because there’s a shittah that ein bishul achar bishul even applies to a davar lach. Clearly, where there is definite bishul, it is assur even al yedei aku”m.