The pool. But it isn't necessarily a problem - your hair, right now, is radioactive. Presumably wouldn't trip a measuring device because it'd be background levels.
The linked report doesn't say how radioactive his hair is or give any indication of whether the person in question is threatened by this reading. Could be bad, could be nothing, we just know it is higher than normal.
For reference, this is about the same in your hair that you’d get from a few hours in a pub in the 90s, never mind working in one - surprising amount of radiation in cigarette smoke from polonium and lead-210.
It does say that. Can you translate that into a measurement of radioactivity & medical risk? I don't think it is obvious.
EDIT The report below it seems to literally be "nothing interesting happened". The thresholds here for something to be reportable are very low. Frankly I don't know why this story is upvoted so much but I'm not about to make a bigger deal about it than one sentence.
