They might have, and despite being more than a thousand years from the printing press, they would've been more or less right.

It's a myth that the Library of Alexandria was the only collection and all sorts of information was lost. Sure, there were a lot of books that probably didn't have many, if any, other copies. But for the most part, most of the books in that library had copies in other similar (if not [all] as grand) libraries.

https://en.wikipedia.org/wiki/Library_of_Alexandria#Historical_background

The Library of Alexandria was not the first library of its kind.[3][12] A long tradition of libraries existed in both Greece and in the ancient Near East.[13][3] The earliest recorded archive of written materials comes from the ancient Sumerian city-state of Uruk in around 3400 BC, when writing had only just begun to develop.[14] Scholarly curation of literary texts began in around 2500 BC.

https://en.wikipedia.org/wiki/Library_of_Alexandria#Decline

Burning by Julius Caesar

Scholars have interpreted Cassius Dio's wording to indicate that the fire did not actually destroy the entire Library itself, but rather only a warehouse located near the docks being used by the Library to house scrolls.[88][82][8][90] Whatever devastation Caesar's fire may have caused, the Library was evidently not completely destroyed.[88][82][8][90]