In regard to the biblical prohibition of mixing meat and dairy there is a dispute whether it becomes forbidden once it is a third cooked (מאכל בן דרוסאי) or even if it was just mixed while hot for an instant (hot means more than yad soledet bo – about 114 degrees Fahrenheit). The reason to say mixing for a moment would be forbidden is that there is a halacha that iruy, a stream of hot liquid, instantly cooks the outermost layer of the food it touches. If so, the outside of the meat that touches hot milk would instantly have been cooked, resulting in a forbidden mixture of meat and dairy.
Practically, there is no difference in regards to eating the food, either way it would be forbidden rabbinically. The only difference would be the question of benefiting from the forbidden food, for example by giving it to a non-Jewish person.