If the crew can remove a secure door by taking off the hinges doesn't this defeat the whole purpose of it being there?
Not so much if it can only be done with relative ease from inside the cockpit, as described by smudgethecat. It was an RJ, so unless Jazz has standards of cabin service not typically seen on such aeroplanes, there would be only one FA*. If he/she was indeed inside the cockpit with the FO, the only "crew" aboard other than the locked-out pilot would have been in the pointy end.
I agree that it's a pretty odd event worthy of further investigation.
*
Now that I think of it, once upon a time I do recall seeing two FAs on an EMB-135. What was the name of that carrier? Oh, yeah, Varig. I wonder how that worked out for them? 