Could be misdirection- if Caesar wanted a friction free removal of the library, he could have burned a load of twigs instead and taken the papers back to Rome- the Vatican archives would be an interesting place to stroll through if so... His subsequent relationship with Cleopatra could indicate some sort of deal or joining of knowledge as well as kingdoms- Ptolemy (her brother whom she married and ruled with) was killed before this, leaving her the sole remaining heir of the Ptolemaic dynasty (300yrs of rule ended with her death in 30BC). A neat bit of politics if you were Caesar- gain an unrivalled resource, end (or absorb) a dynasty in the same operation. Speculation only of course.