Worrisome ... but maybe it's a move to prevent a suspected intrusion ploy.
My house is on a well, not city water. A couple of summers ago, I got an unsolicited phone call from an accented individual asking my permission to put a gadget on my well to "clean" the water.
Duh. No!
Water is the essence of life. Stock up.
My own well is one of the advantages of living in the country.
Did you notify the authorities so that they could investigate your incident to determine whether the intentions were sinister? Perhaps they could have arrested the perpetrator so that he didn't harm someone more gullible or elderly.