Could be undigested food. Could be worms. But even if it worms - whilst it's a bit rubbish to think that you have worms, in the short term they don't do any harm, and treatment is easy.
I would give it a few days and see if you get any repeat of what you saw before. Take extra care to wash your hands. If you see many more, then a trip to the GP may be advisable - but this is not urgent.