They might have disclaimed that because of legal reasons, and the possibility of electrical shock is not out of the question. I think electrocution is very much out of the question though, because when I say shock, I mean 9V battery to the tongue type of shock.
(The following is academic and more for completeness than practicality.)
Just to get some kind of resistance reading I wetted the surface of my shelf and was able to find, in a highly oriented position (this is a semiconductor after all), about 6 megaohms of resistance at 5 mm, or 1.2 x 109 ohm-meters. So end-to-end of a wet 16" shelf, that's nearly 488 megaohms of resistance. That's 120 million times more resistivity than the top heating elements in my electric wall oven have. (Note I haven't measured its resistive impedance specifically, because resistance works well in a general case.)
Since I was already measuring the activity of my oven-bound electron friends, I decided to measure the electrical resistance of my top heating element and calculate the power dissipation. Hence the reference to the heating element resistivity above. I measured the length of my top element to be about 174 cm. The resistance at 10 cm was 1.0 ohm. Using the equation for power (P = V2/R):
P = 2302 / 17.4
P = 3040.23 W
That result quite frankly caught me off guard, because the last time I measured the wattage of my broiler at the meter, it was exactly 3040 W. I wasn't expecting it to be that precise in conjunction with the meter reading. Some fun facts more than anything.
EDIT: I forgot to add "million" after "120" for the resistivity difference.