This is the real science of the so-called "braneworld" scenarios that they're assuming. Gravity lives in the higher-dimensional universe (meaning gravitons, the carriers of the gravitational force, can propagate in all five dimensions), but all other matter (including the electromagnetic field and all other nongravitational interactions) are confined to the 4-dimensional subspace. (In these braneworld scenarios, this is the explanation for why gravity is so much weaker than electromagnetism. We'd never even feel gravity if we didn't have this enormous rock right beneath us.)

So it's only gravitational signals that are able to propagate through the five-dimensional bulk and into the past of the four-dimensional slice. It's straightforward, through gravitational interactions, to get a hand on a broken wristwatch to twitch. It's much more difficult to use gravitational interactions to alter electrical signals in a computer.