The whole point of the article is that Google's sender identity scoring system is more strict when the sending IP is an IPv6 one. That's a pretty clear cut link to IPv6, no?
Google is really strict in general about these kinds of things. I had to go a few rounds with my VPSes before emails from them would consistently not end up in spam, but looking at the headers I'm mostly using IPv6 so I don't draw the conclusion "don't use IPv6" just "if you have IPv6, which is more likely than not now, be careful and read the docs"
Let me rephrase: the whole article is equally valid for IPv4. Being more or less strict is a claim the article makes without proof. And as far as my experience goes, there is no difference.
So standing by it: the article has nothing to do with IPv6 per se.