Kid,
In some ways, it's hard to say.
The shooter is ALWAYS responsible for making sure that they are ready to commit to the stage when they shoot. And remember that while you are under the "guidance" of the RO, you must make your guns safe. You really should have either fired the round or opened the action. For me, the rifle staged with a live shell in the chamber and the hammer back, is the most dangerous of potential ADs.
I guess the RO felt some responsibility, but, in my opinion, the shooter earned a DQ. I think the RO also needs a little brushing up. He made two pretty major mistakes.
Adios,