That's scary. Did you believe there was a problem before hand and that's why he brought in the gieger counter? It appears as soon as it neared the tile on the wall it went crazy but not on the floor or out in the room. Could possibly be the tile, the grout, the mastic (glue) behind the tile, something in or on the other side of the wall, or a cleaning sollution used. Is there more of the same tile or wall materials in another room you could try it on? To be honest I've never walked around with a gieger counter so who knows how many common materials could have a radioactive reading. I do know some, if not all, smoke detectors contain radioactive material (sealed within the unit).
Look on the bright side, if you turn of the lights and the walls glow it will act like a night light!!!
