mike Did you cover a specific eye? I ask because it's my left eye that hurts (probably while looking at temporal dithering, Firefox eye strain type).
I can imagine looking at a screen that refreshes at just 10 Hz could mean it has no temporal dithering in that state. Wouldn't make much sense, but who knows what the engineers did. There's a chance the screen won't have temporal dithering while on 120 Hz, neither - as users would probably see a color difference otherwise as soon as the temporal dithering kicks in. But again, just speculation.
It could also be the screen just keeps refreshing at 120 Hz and they separated the hardware refresh (AMOLED) from the internal refresh rate ("FPS" might be a term for it).