I am no theory expert so my analysis may be completely crazy. However, this is how I made sense of it.
Let's start with the the first triad in the cadenza: Fb, Ab, Db, with the Fb in the left hand. I see it just as a first inversion Db minor triad. Skip the next triad and go to the third triad: Ab, Db, Fb, with the Ab in the left hand. That's a second inversion Db minor triad. Again skip the intervening triad and go to the next: Db, Fb, Ab, with the Ab in the left hand. That's a root position Db minor triad. So you can read every other triad in the cadenza as some inversion of the Db minor triad.
Interspersed with the Db minor triads are the various inversions of an Eb major triad. In fact the second triad in the cadenza is a root position Eb major triad: Eb, G, Bb, with the Eb in the left hand. When I play this cadenza I think in terms of Db minor triads sliding down to Eb major triads.
Now this is where I'm not sure if I'm on firm ground or not, but I think the piece has made a temporary modulation from the starting key of Ab major to Ab harmonic minor. Theory experts may chime in here!