Can a jet engine be restarted after a catastrophic failure?
I have no desire to dispute what a fellow retired 747 captain said, so I'm wondering if there was some miscommunication between you and the captain. 
Or perhaps his definition of catastrophic is different than mine. My understanding of catastrophic would preclude any attempt to restart the engine.

During my time on the 747 I had three engine failures. One simply quit during descent, and I had the flight engineer restart it. One we shut down when the oil pressure started dropping precipitously. There was no thought of trying to restart it as that could well have trashed the engine. Neither of these two shutdowns was catastrophic.

However, on one occasion, shortly after takeoff from Lima, Peru, the #1 engine failed with a loud report, shaking the entire airplane. We were told later that the boom had been heard throughout Lima. The tower reported fire flaring out of both the front and rear of the engine for a few seconds. 
After dumping fuel and landing, an inspection of the engine showed a lot of re-solidified melted metal on the inside of the tail cone.

That was a catastrophic failure.