newtoplanes,
that can be a problem with ARF's. An ARF plane is just like anything else in this world that is manufactured (cars, computers, etc . . .), it's only as good as the person that is putting it together. Somebody could have been having a bad day and didn't attach the firewall in that plane very well. That should be a good practice for everybody that is going to fly an ARF (also applies to second hand planes, even your own builds), check all joints that you can get to and make sure they are secure. If the motor being ran could pull the firewall out, a good tug on it while putting it together should have shown that is was weak.