as far as i know, the red box on some pics is used by russian carriers to secure weapons and other dangerous goods. is is still locked, and damage is minor to it. it is located usually in the read bulk compartment. sure it would show some traces if there were an incident in the rear bulk compartment.
BUT as far as i know the kolavia a321 don't have containers which leads me to the assumption that only compartment 3 and 4 were used, with the rearmost 5 (with the red box) being empty. and usually a full load of luggage fits well into 3+4...
but then again, if it was a bomb, it would not have detonated in the rear section most probably. and even the bulk section 5 is located under the rear three rows.