The aerodynamics can be explained, something I cannot do for that quote. Let's address the quote story first and, once that's out of the way, let's have a look at the aerodynamics.
Vortices rotate, so they have rotational energy. That has noting to do with propulsion. Hurricanes, Tornadoes, ... are vortices, even pulling the plug in average Joe's bathtub and letting the water circle is a vortex and hence contains rotational energy. No propulsion there. (The rotational energy comes from other sources).
Thrust is not an "additional requirement". It's just that in stationary, horizontal, and level flight, thrust and drag are at equilibrium. But that's total drag, the induced drag is just a part of that.
Bottom line, I cannot support that quote.
Induced drag (slightly oversimplified) is just the tip circulation of the wing. Basically, under the wing the aircraft needs higher pressure than above, that's what is creating the lift. But as a parasitic effect, that means that during flight, there is also some air flowing around the wing tip - basically pushed from the high pressure domain below the wing to the low pressure domain above the wing. So around the wing tip, strong vortices are induced. Now, for each meter that the aircraft flies, one meter of vortex is added on either side. These vortices contain kinetic energy, and for lack of another source, it had to be provided by the aircraft. Finally, if you consider that it is "energy spent per distance", and the very definition of energy is force*distance, you can divide that energy by the distance and retrieve a force - the induced drag.
That's the case for any wing, glider or jet fighter, propulsion doesn't change that. The point about gliders is only that they provide that energy by losing altitude.
Then there's a bit more theory on that, if you're interested
and also, the vortices aren't necessarily only two simple vortices on either side, rather they are a spacial distribution, described as a vortex field. But that's just to add more precision, not to change the picture.
They're all very great, btw
As for what you see on the 747 - it's not 4 vortices, it's four vapor trails, that roll neatly up into the vortices.