Th black box usually isn’t in the cabin. Not sure about 777 but IIRC most BB equipment is located toward the tail because that has a better chance of surviving impact.
He’s saying that if the cabin remained intact, then there would not have been a situation where the black box would have been damaged either. In other words, there’s not the type of conditions in the crash where it — too — would have been damaged.
In 1953, when I was twelve years old and was a newspaper delivery boy, I went down to the train depot every morning to get my shipment of papers for home delivery. During a period of time when there were several crashes of airplanes, the paper would print a picture on the front page of the debris field of the plane, which usually burned after the crash and the cockpit voice and flight recorder were never recovered intact. But I noticed from the pictures that the tail section of the airplane almost always survived the crash and fire with little damage. I then wrote a letter to the Civil Aeronautics Board, which was the precursor to the FAA, suggesting that the black box be placed in the aircraft tail section to improve survival of the recorders. Several years later I received a nice letter from the FAA saying that they adopted my idea. When I was three years old I lived next to an airport in Portland, Maine, and I witnessed a plane crash and fire which killed several people in a trailer park next to the airport.
The way I read the remark, his use of the word “cabin” is better translated to “fuselage.”