This voice is one of the 100 or so in the Genos Preset/StyleVoice category.
Confirmed! There are exactly 101 hidden voices ist the StyleVoices category.
I don't know why these voices are hived off in their own category, and they are not listed in the Genos Data List. Perhaps they are to ensure compatibility with styles from earlier models?
I don't think it's to enusre compatibility with earlier models. That's what the Legacy voices are for.
One half of these StyleVoices are (by the majority) S.Art2! voices or Live! voices. I didn't analyze each of these voices, but for quite a few S.Art2! there is an obvious reason. Those S.Art2! voices have a sampled vibrato built in, that will sound automatically a short period after pressing the key. This may (or sometimes may not) be useful for a solo voice, but this a deal breaker in a (accompaniment) style voice (RHY, PAD). So what Yamaha did here was to copy an modify these S.Art2! panel voices to make them suitable as style voices, by eleminating the automatic vibrato.
Recall that Yamaha does not allow us to fully edit S.Art voices, neither using Voice Set editor nor YEM. Therefore it is unknown, which individual changes were made to these voices (besides obvious ones like the vibrato).
I have no idea why Yamaha insists on hiding these voices, but they even insist on hiding XG / GM2 voices (which were available in the Tyros line), don't they?
BTW, the second half of the hidden voices are Organ (Flutes) voices.