“He IS saying that at least one part of the dread prophecy was fulfilled: Jerusalem was smashed, the Temple destroyed, and not one stone was left upon another.”
That’s an entirely different prophecy, not found in Revelation, so that can’t be what he is talking about.
Jerusalem, the great city, the holy city, was utterly destroyed. 1.2 million Jewish people lost their lives in the conflagration. Jerusalem was burned, and when the Romans were finished, not one stone was left on another. Jesus had warned of this day in the Mt. Olivet discourses (Mark 13, Matthew 24, Luke 21) and had wept over Jerusalem: O Jerusalem, Jerusalem, killing the prophets and stoning those who are sent to you! How often would I have gathered your children together as a hen gathers her brood under her wings, and you would not! Behold, your house is forsaken and desolate (Matt 23:37-38).
He's not just talking about the Book of Revelation.
The destruction of Babylon is not only prophesied in Revelation, see for example Isaiah 13. The prophecies about Babylon seem to include a number of Babylon types, although the final calamitous destruction will take place once, to the “real” Babylon. I think he is saying that Jerusalem was a type of Babylon and therefore suffered a type of destruction that it was in no way the destruction that will be suffered by the real Babylon. But his point, how Jerusalem can be considered a type of Babylon, is very interesting and scripturally sound.