It's obviously made up. Rappelling this way would not work and you would have a good chance of killing yourself.
When rappelling with an ATC you lock the rope off, and control your speed, by pulling the free end of the rope downward. Feeding your slack out of a backpack you're wearing would force your hand upward as the slack came out and the rope started to bind on that tiny hydration hose hole. If you're lucky the whole system would lock up; if you're not lucky you'd lose control of the rappel and fall.
For future reference the way to rappel with a rope is to stack it into the pack, open the pack up nice and wide so the rope will feed freely, then clip the pack to your harness with a sling so it hangs below you. Or use a rope bucket, which is expressly designed for this purpose.
I didn't read the blog post as a step by step instruction, more like some commercial for the bag.
I've done quite a few rapells and sometimes keep my rope in my closed rope bag on my back (with compression cords in place) if there is a large risk of the rope getting entangled with the environment, I'm on a bridge over a road or I'm on a cliff above salt water.
I use a french prusik on the rope below the ATC and pull the rope out of the bag at the same time as I pull down the prusik. Often the rope gets slightly stuck, a harder pull on the rope has freed it for me every time and I never take care when putting the rope in the bag so I would think a proper packing of the rope would decrease that risk a lot. Should the rope get really stuck I would simply take off the bag and open it up while hanging in the harness. Not a big deal at all.
Have you tried clipping your bag below you, like on a sling off your harness? It takes only a few seconds longer to set up that way, and the rope feeds pretty easily because it's coming out in line with your brake hand. It's also a bit more stable because the weight of the rope is on your harness instead of above it (as when you're wearing the backpack).
When rappelling with an ATC you lock the rope off, and control your speed, by pulling the free end of the rope downward. Feeding your slack out of a backpack you're wearing would force your hand upward as the slack came out and the rope started to bind on that tiny hydration hose hole. If you're lucky the whole system would lock up; if you're not lucky you'd lose control of the rappel and fall.
For future reference the way to rappel with a rope is to stack it into the pack, open the pack up nice and wide so the rope will feed freely, then clip the pack to your harness with a sling so it hangs below you. Or use a rope bucket, which is expressly designed for this purpose.