In the same breath, they insinuate that Google both sells and uses DNS usage from their 8.8.8.8 and 8.8.4.4 resolvers.
Cloudflare is somewhat right: Means, Motive and Opportunity - but for a conviction you have to prove someone acted on the Opportunity. The Motive of Google is tampered with severe risk for loosing trust.
Cloudflare can make an argument they are fundamentally better positioned and that is all they do. As with all US based operations the NSA may cook up some convincing counterarguments and we may never know.
The OP did not say that cloudflare is "saying" that. The OP very clearly said they are "insinuating" it. And yes under the heading "DNS's Privacy Problem" the post mentions:
"With all the concern over the data that companies like Facebook and Google are collecting on you,..."
I think that juxtaposition of this statement under a bolded heading of "DNS's Privacy Problem" is very much insinuating that.
I don't think it's intended to say anything about Google specifically. Keep in mind that there are many other DNS services out there, and some of them are known for being pretty scummy, e.g. replacing NXDOMAIN results with "smart search" / ad pages.