Why is the chosen length a short novel? Books range from a few pages to hundreds of pages.
If we make some unlikely assumptions - that there were 10,000 students attending Nalanda every year from its foundation to its destruction, and that each student wrote for only 1 hour a day, 5 days a week for 40 weeks of the year, that gives us 2,000,000 hours of writing. Over 763 years that is 1,526,000,000 hours.
There were 2000 teachers at Nalanda, that's 400,000 more hours per year, 305,200,000 hours over the course of Nalanda's existence.
The population of India in 1000 AD is estimated at anywhere from 75 million to 200 million. Not all the students would have to write all the books as there was another university nearby that was also destroyed by Muslim invaders called Takshashila[2] which would've also housed and produced books, some of which no doubt made their way to Nalanda, and show that books weren't only produced in one part of ancient India, and that there was a large enough population to support a book "industry" with things like quills and ink (they actually used a knife with palm leaves that could last hundreds of years[3]), let alone writers.
Add to that, what are some of the students going to be doing once they graduate? Writing books. As that last link says:
> Hindu temples often served as centers where ancient manuscripts were routinely used for learning and where the texts were copied when they wore out. In South India, temples and associated mutts served custodial functions, and a large number of manuscripts on Hindu philosophy, poetry, grammar and other subjects were written, multiplied and preserved inside the temples. Archaeological and epigraphical evidence indicates existence of libraries called Sarasvati-bhandara, dated possibly to early 12th-century and employing librarians, attached to Hindu temples. Palm leaf manuscripts were also preserved inside Jain temples and in Buddhist monasteries.
That is all to ignore that movable type printing was invented in China[4] before Nalanda was sacked, and that scholars from all over Asia went back and forth from Nalanda sharing texts. You might have heard of the Journey to the West, which was inspired by an actual journey that was written down in a book called Great Tang Records on the Western Regions[5]. In it, Nalanda is mentioned because Xuanzang, the author, visited there. That book took 2 people to produce, and is described as:
> The book contains more than 120,000 Chinese characters and is divided into twelve volumes
That's in 646 AD. I think you underestimate the abilities of the people of that time to produce books.
[1] https://history.stackexchange.com/questions/33640/what-was-t...
[2] https://www.britannica.com/place/Taxila
[3] https://en.wikipedia.org/wiki/Palm-leaf_manuscript
[4] https://www.history.com/topics/inventions/printing-press
[5] https://en.wikipedia.org/wiki/Great_Tang_Records_on_the_West...