The Foxface is incredibly resistant to ich and some external parasites. They have a thick slime coat that has been said to have properties that repel ich to a certain point. That said, the fact that fish have been introduced to the tank without QT means that ich is likely present in the tank. You may want to take the "wait and watch" approach here. Observe carefully to see how long it takes for the white spot to go away. 3-5 days and it's likely ich. If it goes away within hours, then it's likely just debris stuck to the slime coat. Watch for behavioral symptoms from all the fish such as: flashing/scratching on things in the tank, heavy breathing, excessive hiding, swimming into the flow of powerheads or returns.