That would be quite ironic :)
I dont see it though, would you mind pointing it out? Are you talking about spellling, because that one is intentional (and even underlined) to show an example.
As a non-native speaker, I thought the correct form would be "Fast, working pages mean better rankings.", "mean" in singular. I checked it against a grammar app and it said the same, but I see how it could be used in plural for the header, as in "having fast, working pages means...".