So they are using the motors from the printers as generators.
You still need to rectify the voltage to store the energy in lead acid batteries, losing precious voltage in the diodes. I wonder how they get the >13V to charge the batteries.
On the:
>Are the motors AC or DC?
part, I believe all printers I've taken apart in the last decade used DC motors of some sort (with the odd stepper thrown in).
This would never have been possible without the Internet. One might have found stuff like this in the Whole Earth Catalog, but it would likely never have reached these people.
On the other hand, one could say the same about drone attacks by ISIS, or the recent one against President Maduro. And that approach will likely become commonplace.
Necessity is the mother of invention (and cell phones are so ubiquitous they probably have at least one or two with internet).
You will see more of this as the worlds trash piles up. There's value to be had in there for the poor and destitute (not saying this is good or bad, it just is).