Not sure if I'm missing a joke, but the whole point of the analogy being a treadmill is that there's nothing to fall down. Regardless of positive (running forward) or negative (going backward on the treadmill) life changes, your happiness will probably stay relatively consistent because you're on a treadmill and there's nowhere to go.
The live out of a backpack lifestyle is definitely a unique way to experience the modern world and I'm sure it's fulfilling for the author, but you can even tell in their post that life caught up with them somewhat and they needed to start staying in one place a little longer in order to maintain social relationships. Their linked post about walking every block of Manhattan and tracking all of their movement since 2015 feels like the exact opposite of a minimalist lifestyle and it seems to me like they live out of a backpack not out of some anti-materialism lifestyle, but instead just as a practical way to fuel this obsession with traveling and tracking.
I admit, I've seen the author's Instagram story about walking 100k steps in a day in NYC and watched the whole thing because it's interesting, but I also take that and posts like this with a grain of salt. I'll happily take my horde of shit I need to get rid of in the garage over obsessing about how I can optimize tracking my every movement.