I suppose it still counts as a stone that has a direct effect on evolution, unlike others such as Icy Rock, etc.
That said, on reflection King's Rock could use some consideration as well.
In retrospect, I would've left it at nine: the stones that you literally have to select out of your bag and use to evolve a particular Pokémon. I was confused even more when the video explicitly rejected the Oval Stone, yet kept the Everstone, despite the fact that both affect evolution in some way and are both held items. When I first started watching the video on mute and only saw the stones' graphics, the Everstone just stuck out to me like a sore thumb.
As for the King's Rock... dealing with held items (Metal Coat, Dragon Scale, Razor Fang, Razor Claw, etc.) would just change the whole subject to just evolution via items in general. But again, Everstone is also a held item so ¯\(°_o)/¯
I suppose that's feedback that can be passed to the creator Disaster Strikes. (Video was out before the article, and it was a user-submitted content rather than made entirely by the SMT team). Fair comments I suppose with the Everstone being included over the likes of the Oval stone, when only nine are direct evolution methods (unlike the Oval stone which requires being held + levelled).