Unsurprisingly Google actually does also have IPv4 addresses. What they're measuring isn't "How did you reach our servers?" but instead "Could you have reached our IPv6 servers?"

So that measures everybody who has working IPv6. https://www.google.com/intl/en/ipv6/statistics.html

> We are talking about being issued only IPv6 addresses where you actually use it to connect to stuff.

You seem to be asserting that dual-stack machines use IPv4 by default, but that's not really true. If your machine has both IPv4 and IPv6 connectivity, browsers will in fact use IPv6 to connect to sites that support it, like Google. They prefer IPv6 by default and fall back to IPv4 if IPv6 is slower (Happy Eyeballs algorithm).

Of course, random software can mostly use whichever it wants, so I'm not claiming every process on such a machine will use IPv6, but most common stuff does.