Hopefully all will get resolved here but without even looking to see the damage I would say that it was the mounting studs that failed?
If that is so the most likely cause of failure there would be 'excesive' valve lift, more then the 'rocker arm asssembly' was tested at handling.
My personal experience would say that if you are over .600" lift, then that was the cause right there.
If that is so, then it is the engine builder that is at fault for specifying the cam.
Some engines for the street are being built with the same approach as a flat out race engine. That means every component is stressed to the maximum or as Dolly said, 'this is what happens when you put 10 pounds of mud in a 5 pound sugar sack'.
My personal opinion is that no component should be stressed to more then 85% of its yield point. That is a reasonable safety factor. .85"mue".
.85 x .700 is .595. You certainly can push it to the limit but when it breaks it is over the limit.
If you reach 100% of your heartbeat capacity you are dead. Morto.