There are quantum(-specific) phenomena that contain true randomness -- i.e. no amount of knowledge will make the result more predictable.
Those phenomena get harnessed to interact in a certain way to produce use computations. Such devices are quantum computers.
But if you just want the randomness, you don't need the computer part. You just measure the quantum phenomena and don't bother to make the interactions happen in just the right way to do (other) computations. The "computer" part is irrelevant for that use case (random number generation).
By analogy, this sounds like "how to turn a (classical) computer into a heater". Same issue: running a current through a wire creates heat. Certain setups of said wires also produce useful computations. But if you just want the heat, you just need a regular boring resistor; you don't need to make it into a computer as well, though you're free to use whatever heat it throws off as well.
Edit: Okay, on further reading, that is what they mean by a quantum computer: one that just takes such measurements and where you can specify a distribution it samples from. But, just to clarify, this is not the kind of quantum computer you hear about generally, where it solves factorization or simulated annealing or something.
As in the quote from Scott Aaronson, it's not the most interesting thing you can do with a QC.