That's odd. I looked at the video you linked, and all I saw was government JBT's shooting. Maybe I missed it. Is there a point on there where it's clear that the BD's are shooting? In fact I think almost all of the deaths among the thugs were "friendly fire" Several were killed by a grenade that one of their fellow goons threw in the room with them.
Davidians fired first through the wall of the building at ATF agents outside. The rest is history.