Yeah I checked some tracks and it basically looked like the longer someone spent in a place, the higher the readings got. Maybe when the device doesn't get a lot of ventilation it starts to misread.
Or they zeroed in on something interesting, since finding interesting radioactive bits is the primary use of the device. One I saw in CA was confirmed to be a uranium deposit, by geological survey, on a random trail near some houses.
If you don't believe any of this naturally occurring phenomenon for some reason, there are several YouTube channels that check out these places, and try to find their own high activity areas/objects. There also subreddits dedicated to it,'and even a map where you can find places! ;)
I wonder if this explains why many of the higher radioactivity sites in my state are hotels.