If you wish to not have the callsign DataHub, you can untick the "Tag AIS " in the OHA settings in the DataHub
The boats close to you that are picked up by your onboard AIS should not have the callsign DataHub.
The only AIS that is added to the network are the ones your local AIS doesn't have there.
You could check that it is working by disabling AIS from Internet in the DataHub, then check if you are getting AIS updated locally on your chart plotter from your AIS unit.