at a picnic I wouldn't eat meat grilled cause kuffar used them. Someone said fire cleans it so if the kuffar put pig on the grill the fire would clean it

What I dont understand is that there may be burnt bits of pig, and they were saying its pure. Is it only purified by fire if it is burned to a crisp cause otherwise how could we use the grill? 2. Does heat from a burning iron cleanse the same way as heat like in a stove or oven? 3. How come I only hear one dialect of Quran, why did Othman burn them if the other dialects were allowed, and did Rasul Allah have to memorise each verse in each dialect? Sorry for the questions. Jazakm Allahu khayran