It's a contrived distinction. If network effects, like Facebook enjoys in social media, keep out competition, you're a classic economic monopoly.
Also, why use such a heavily loaded and overloaded term? I am sure he had his reasons, maybe because it is ambiguous.
I'm pretty sure we all agree that standard oil and internet explorer were not of great benefit to society.
Distinguishing between "good" and "bad" monopolies is sufficiently complex to deserve more in-depth exploration. Thiel is smart enough to realize that which is why I consider his point to be misquoted. Unfortunately, his view is oversimplified so as to be readily consumed and debated.
He lists characteristics of a monopoly in his book: proprietary tech, network effects, economies of scale, and branding. First mover advantage is mentioned as a "tactic, not a goal" - a chapter is even called "Last Mover Advantage." Google, for one, was clearly not a first mover in the search space.