Unless some new changes have been made, there are no sensors in the rear of a vehicle to tell the airbag to deploy. Your back and neck will hurt regardless if the airbag had deployed or not. As previously mentioned, airbag deployment when the front of the vehicle has struck something depends on a number of factors that the sensors and computers calculate. You likely did not meet the parameters for deployment.
Looking at the pictures of your accident, I would say that you were hit at the most 30mph and that comes from pics shown by EMS when they transport patients to the ER to be check out. I am curious as to why your engine is shot as I didn't see a picture of the front end.
Glad you made it out ok.