As for the air bags not getting triggered, that is not unusual for them not to deploy in a REAR collision. The forward force was likely not enough for the computer to consider the incident serious enough to deploy (as it should since there is the possibility of injury from air bag deployment).
Clearly, you will need everything throughly checked out. Getting errors about the restraint system definitely warrants investigation and an explanation. Sounds like all of the safety feature did their job, but don't know why that would trigger an error.
2013 X3 28i (prem, tech, cold1&2, conv, hud)