NB: this is not "IPv6 traffic crosses the 50% mark" but "availability of IPv6 connectivity among Google users", which is a very important difference. This means roughly half of Google users have IPv6 capability, which does not 1:1 correspond how much traffic is actually transferred over IPv6, which is what this submission says in the title.
Yeah and this distinction explains the fact that because China's Great Firewall blocks Google, this website shows 4.66% adoption as a reflection of that. I think China's IPv6 support rate is actually much higher than that, maybe a little over 50% because of its central initiative to increase IPv6 adoption?
Right, but in most situations clients will prefer IPv6 if its available, so if they have access, they almost always are using it, at the very least from their local network.