I do believe it is a deliberate strategem for optimizing the "oomph" of a certain dance rhythm or phrasing. It certainly isn't bad technique. This guy has more chops, virtuosity and elan than everybody on this thread. Not to mention that a unisonoric accordion can be played as easily in one direction as the other, so what would be the problem. Articulating the air more frequently does give a certain movement or lift to dance playing, which may be the purpose of enforcing that by keeping it snapped at one end. It is also true that for reasons unclear to me, free-reed instrument valves swell more freely and supple-y on the pull than the push, these walzer guys may prefer that feel.
Many fans of tango bandoneon are unaware that the classic and prescribed bellows articulation among the Argentine tangueros is to play on the pull, using the air button to close the bellows between phrases. And to do so at strategic spots complementary to the whoomph and movement of the dance.
There have been disdainful comments from uninformed quarters opining that Argentine tangueros play on the pull because they are too lazy or limited to become bidirectionally fluent in the fiendishly difficult, randomly placed, multi-octave pull layout and push layout of the bisonoric bandoneon to play it on the push as well as the pull. Generally, however, this disdain is misplaced. The reason for playing on the pull with busy air-lever use relates to dance rhythm as well as that suppleness of air-valve swell in the pull direction.
Interestingly, players of unisonoric bandoneons as used for tango in France and by some other non-Argentine players, achieve the "proper" Argentine tango phrasing by playing their unisonoric bandos the same way--on the pull, using the air release at strategic points complementary to the dance movement to close the bellows and start the next phrase. They're not doing it because they are lazy or inept, as a unisonoric instrument doesn't require any different fingering or note layout for the push versus the pull. They are doing it to get that authentic tango feel.