Cats usually don’t have diarrhea, at least not when they’re healthy. When it shows up, it might be a sign of an internal problem, probably digestive. If the episode of diarrhea is short, it’s not a problem, and it might be caused by something in the food or water. As soon as those substances clear its system, the cat should be fine.
See more here:
Cat Diarrhea Causes and Remedies