My understanding has always been that Bioweapon mode uses both fresh air intake and recirculate in the same style of most new "tight" homes. I want to be clear that I could be wrong about this, but having built a foam insulated home, we had to ensure positive pressure. To do so, our air handler would not only recirculate house air, it had an inline fan in a dedicated duct to the outdoors. That fan ran during specific times when the air handler was active, thereby forcing outside air to be filtered and distributed into the house. It made little sense, however, to draw in outside air only. You have filtered, conditioned air already in the house. To add more particulates into the filter and have to recondition outside air is an extremely inefficient practice.
Vehicle cabins are much smaller. But many of the same principles exist, which is why I have always assumed Tesla is doing what is industry standard in homes today.