If this happens again, smell the wet spot (I know, gross, but you know what urine smells like). My guess it was urine. If this persists, a checkup by the vet might be in order. Male cats are prone to urinary tract problems. Also check that he is not urinating frequently or straining while he goes.
I would say that you need to watch Fluffy and see if there are any litterbox accidents. You may not know if he is finding elsewhere to pee. He could have a UTI which left untreated can become quite threatening.