I think he meant that it was not supposed to be "Mac Oh Es Ten Ten Nine Two", but rather "Mac Oh Es Ten Nine Two" when referring to Mac OS X 10.9.2. Do you think people said "Mac Oh Es Nine Nine One", or "Mac Oh Es Nine One" for Mac OS 9.1?

I think you write (and say as /ten/) "X" as the major version if you're also using the non-numeric minor version: "Mac OS X Snow Leopard"; but you omit it when using the numeric minor version so as to also use the Arabic major version: "Mac OS 10.6". You say /ten/ either way and never twice.

People seem to quite commonly write "Mac OS X 10.6", which duplicates the 10. News articles and Wikipedia included. I don't remember what the machines themselves reported, though. I don't have anything pre-Sierra anymore.