Unknown unless you have a time machine. Guns jam, knives don't. There's plenty of vids where a gun jams in illegal activity and in self defense. #nuance #objective
What he's arguing is that a mass casualty event can be more effectively executed with a firearm than a knife. Since mass casualty events usually involve panic, people running away from the threat and nobody trying to stop the threat, the effectiveness of the firearm is more a function proper application of the right tool for the circumstances.
But to kill 4 college kids asleep in the same house, a quiet knife used on a stationary/sleeping victim is a much better choice.
He's comparing different tools with one being better suited for one application versus a different application. Had the killer used a firearm on those sleeping students, the sound would have caused some to flee or hide and call for help. Others hearing the sound could also come to their aid.
The only way his statement is true is if we ignore reality and the choices people make when planning a mass killing.
The worst mass murder events in recent US history used no guns at all: 9-11 and the OKC bombing.