In The Great Gatsby, what is the significance of Owl Eyes in the library?

One afternoon, not long after he has moved into a rented
house in West Egg on Long Island Sound, Nick Carraway receives an invitation to one of
Gatsby's nightly and infamously decadent garden parties. Seated with some of the
intoxicated guests, Nick hears outlandish rumours about his incognito host: That Gatsby
is related to Kaiser Wilhelm of Germany; that he once killed a man; that he spied for
the Germans during the Great War; and that he was a graduate of Oxford University.
Later, touring Gatsby's house with the narcissistic Jordan Baker, in the library he
happens across a bespectacled man he nicknames "Owl Eyes". Although certain that Gatsby
is putting on an elaborate charade, Owl Eyes is amazed that the books in the library are
real. But he reads that as well, comparing Gatsby to a "regular
[David] Belasco", an American theatrical producer and impresario, famous for his highly
naturalistic stage sets.