While I can’t speak for what Bkool’s software does differently, Zwift treats the Bkool trainer like every other ANT+ FE-C or Bluetooth smart trainer: we read the power they are transmitting to us and use that figure to determine speed within Zwift.
It seems like their latest firmware has introduced some issues between their hardware and Zwift that did not exist before while trying to address the ‘ERG’ mode issue.