Yes, it could be parasites, it could be an infection, it could be harassment...it could be anything. In the absense of further symptoms, I do not recomment treating a fish when you have no idea what the problem is. Close observation over the course of the next 24-48 hours are in order, not random treatment for an unidentified ailment.
If you do not have a separate hospital tank, however, you could be working on getting one in the event that the necessity of threatment is imminet. Whether this fish will need a hospital or not, it is a very good idea to have a separate hosital/QT on hand so that it is available when needed.