I'm not even sure why a FAQ would be needed for this - the rules themselves seem pretty clear to me:

1. Models in a transport are destroyed if the vehicle is destroyed and they cannot disembark.

2. Models cannot disembark from a vehicle that went flat out this turn.

3. Vehicles are destroyed if they are immobilized after they moved flat out on this or the previous turn.

So, if your transport goes flat out and is either destroyed or immobilized in the same turn (i.e., your turn), which can pretty much only happen if you ram/shock something or fail a dangerous terrain test, the models cannot disembark because of 2., and are destroyed. In the opponent's turn, if they manage to destroy the vehicle or immobilize it (and thus destroy it because of 3.), the models are allowed to disembark (and thus don't get destroyed), because 2. only forbids them to disembark if the vehicle went flat out in the same turn as when they disembark, not - as in this case - in the previous turn.