When non-Jews prepare food, they are not constrained by halachic considerations. For example, we are prohibited from using a non-kosher כלי שאינו בן יומו to cook our food. But בדיעבד, that food is permitted.
What is the status of food cooked by a non-Jew in a כלי שאינו בן יומו?
As usual, sources are available through the links.