The idea is simple ~ the Arabs who found themselves owning ancient cities filled with scholars of all sorts decided to make themselves look to be at least their equal by inventing Islam.
That's why the Koran appears in Arabic (?) a full 150 years before the next literary work in Arabic ~ BTW, the Koran appeared mostly in Aramaic ~ see the work on pre-dot Arabic, and the earliest Korans. That lends credence to the idea the Arabs pieced it together out of materials they encountered in Damascus, not Mecca.
The claims of Mohammad meeting Ethiopian Christians are simply to throw doubters off the track regarding the true origins of the Christian writings incorporated into the body of the Koran.
Interesting.