Is the USB data between Boson and application strictly RS-232?

It’s not RS-232 at all. RS-232 is an electrical specification. For Tau2 cameras, the VPC converts USB transactions to RS-232 which is then fed to the Tau2. Boson has built-in USB, so it takes USB unconverted. Commands are transferred over a virtual serial port over USB, so it is basically the same concept as the communication for Tau2.