That's ridiculous. Heat pads work very well for pacmans. The trick is to use your brain. What does a lamp do? Remove humidity! These are amphibians. They like water.

If you use a heat pad, you put it on the side of the tank, to increase ambient temps, while allowing the frog to burrow to escape the heat.

Its common sense not to put it on the bottom if you know anything about the natural history of these frogs.