The author doesn't seem to have an open source mobile app or anything that would allow them to source the data from devices themselves. I'm curious where the data was collected from, esp. if it was opt-in (at the collecting device)
I haven't built any apps for contributing to beaconDB as of yet. The website links to NeoStumbler and TowerCollector, which are Android apps that can be used to collect this data.
It is rather surprising how many people have started contributing already. I believe that people want to support alternatives to big tech so they aren't completely reliant on these providers, and beaconDB is currently the only database not owned by big tech. Not 100% sure that answers your question :)