From the reading I've done on line, there probably aren't a lot of officers yet. The officer I saw looked around 50, but his uniform and hat were clearly not APD.
Maybe some of the APD officers who resigned from there got hired by the Transit Police.
The transit system in greater Boston runs on an EDACS Pro Voice system and there are two PD talk groups. The PD however operates on two UHF T Band channels, but also on the MA State Police system. So, it wouldn't be a surprise to me if the Cap Metro police run on GATTRS while the rest of the system runs on LCRA.