There is not a lot of easily digestible information about dry bronchiectasis available. It was first recognized nearly a century ago, but research regarding it is sparse.
If you feel like doing a "deep dive" into some technical explanations, try this article:
https://www.mdpi.com/2077-0383/5/12/115
I believe the European Lung Federation/Association has something recent to say about it, but I cannot find it right now.
Sue