The "circumvent" part is that Facebook's content isn't indexable by Google. For example, a website review on Yelp winds up on Google, but a review from Faceboo

The "circumvent" part is that Facebook's content isn't indexable by Google. For example, a website review on Yelp winds up on Google, but a review from Facebook won't show up. Insofar as they're creating content in a walled garden that Google can't access, they're circumventing Google. (It might not be the best usage of the word circumvent, but I still think it's clear what the author is going for here)