I'm surprised to find that author of such excellent books about FM and DX synths writes that all Yamaha synthesizers before FM-X arrival have used only sine wave in the operator. What about TX81z, DX11, V50, SY/TG77, SY99, FS1r?
... you may be able slide by saying the TX81Z's extra waveforms are still based on sine waves (halves or quarters of the sine wave phase shifted and pasted together). But when you get to the FS1R - that's the "same" implementation as FM-X for voiced waveforms. I'm not aware the FS1R called this "FM-X" and FS1R predates Motif Classic by 3 years.
I'm not sure this historically inaccurate trivia detracts from the meat in the article. It could have been lost in translation by the document writers/web crew - so it may not even be Massey's fault.