There are offline OpenStreetMap clients, but there aren't ways to update said map offilne, or to create "mini-OSM" that later can sync with the main one.
For instance, if you're doing a survey in Amazon with a local community, you would need to make a survey, go back somewhere with internet, sync the data with OSM, download the new file and go back to the local community.
The innovation those guys are making is to create a mini-OSM, so the village could have its own mini-OSM, and later that mini-OSM could be synced to the main one.
They are not the only ones trying to do that, an NGO called Digital Democracy is also trying (https://digital-democracy.org)