Yep. It stores extra air between the output of the reg and the input to the dump chamber.
I can theoretically see that as maybe improving shot-to-shot consistency a tad, since there's now a bigger "buffer" of regulated air to pull from the moment the on-off opens up again, but there's a big difference between theory and fact.
After all, the Magic Box itself was supposed to add range, consistency, accuracy, two inches of length and an inch or girth, all that sort of thing, when in fact it did pretty much zilch.
Might be worth an experiment though. Try it over the chrony and at a target range both with the 'volumizer' attached, and then again (with the same paint under the same conditions, etc.) with the thing removed and the hole plugged with pipe plug.
Record the chrony readings and whatnot, and do a proper comparison.