Those neon screwdrivers are excited very easily, not only by 50/60Hz power lines but also by proximity to strong RF fields.
By the way, I heard of a story some time ago of an apprentice who dropped a neon screwdriver into water, then fished it out, shook off the loose drips and put it back in the toolbox. The next guy to use it got quite a shock, as the water had gotten inside and partially shorted the series resistor.
