Osmand does not have and display "own" data. It works and displays data of the
openstreetmap.org project.
Refering to bnb it might use the tag tourism.
see
https://wiki.openstreetmap.org/wiki/Key:tourismYou are welcome to support this project and add information which is not already accessed.
In OsmAnd you can use the search for inestigate for accommodation, you also can create subcategories in search.
Just "play" around with OsmAnd to understand what it can accomplish.
Peter