HA2NON
If there's an incoming call from the network with the callsign for ex. "ABCDEF" (which is not in the DMR ID/callsign database), then the openSPOT4 does not know what DMR ID to use when it translates the call to your DMR transceiver, so by default it uses the openSPOT4 owner's DMR ID.
You can see more information about this process if you look at the device log on the Status page (make sure Advanced mode is enabled at the bottom right of the web interface to see the device log).