When Doujima said 'one more came', does this mean it is a mixed bath? Or more likely, another male student finished earlier than Yukihara, but then again he comes to the conclusion that Erina finished before him.
It really could be either way, if he finished 5~10 minutes earlier, he could have seen a naked Erina.
Next chapter, Megumi couldn't sleep at night, messed up ingredients or so the next day and was fired. Shokugeki coming!