Dirtbagging doesn't necessarily entail living outside. Could bum a room for a while. See https://en.wikipedia.org/wiki/Dirtbag_climbing for context.

To clarify: I tend to think of living out of a 40L pack as a dirtbag thing rather than a nomad thing... most of the nomads I know just use hard shell luggage, including me when I hotel hop (I've had nice expensive backpacks destroyed by bag handlers, so hard rollers are better). OP mentions that thy don't have to check their 40L bag; I've always ended up with mine checked but I guess splitting the load into a second personal item could make that less likely.

The focus on "packing" there is on weight/volume minimization - for example backpackers have been known to shave down the handle of their toothbrush to save a few grams. That sort of thing.