That's the sticking point.They both almost did in fact use it on China...
USSR wanted to use nukes for the border dispute
McArcther wanted to nuke China to win Korean war
They "wanted" to. But they didn't despite China not having nukes.
So why should china emphasize on this so much now?
Or is it that, even if they "wanted" to use it on China,they couldn't because either china had some form of deterrence through other means or US,USSR had some kind of technical obstacle to do that?