Then I think this is a trap to get some kind of proprietary app onto your phone.

The clock could set itself from radio signals: standards-compliant.

The clock could have WiFi or Ethernet and use [S]NTP: standards-compliant.

The clock could have a SIM and use NITZ: standards-compliant.

But BT it is. So now rather than having a dependency on standard or generic resources, it requires a BT pairing with the right kind of phone Ridiculous.