I believe he also mentions in there that it couldn't have been a fire or else there would be plenty of radio traffic. You admit you doubt the zoom-climb, but this scenario described by McClaine doesn't fit with the spontaneous explosion, either.
Correct about the fire, but there would only be radio traffic if they knew there was a fire. What if there was a fire somewhere on board, (maybe contained), that they didn't know about? I mean, were only talking about 5-10 minutes here...That would fit the fuel tank explosion. Similar to a car in a crash that continues to burn until the gas tank explodes.