There are three radios in the hub; WIFI, BLE, and 915/868mhz. The WIFI and BLE radios are built into the main processor but the 915/868mhz radio is a different module. The reboot count in the radio_status field is the number of times the 915/868mhz radio has been reset. We track the value across all the hubs to make sure we didn’t introduce a firmware bug.
Hope that helps.
-Rob