Okay, no problem, but they’re repeating a story which isn’t true. Caesar himself wrote that the fire spread to the dockside and to “some books which chanced to be there”. His vantage point was the citadel, which is where the Library was located, making his description (the only surviving eyewitness account of that fire, AFAIK) incompatible with a later account. Some ancient nimrod who didn’t like Caesar (name escapes me) bears responsibility for starting the spurious claim. The Library wasn’t destroyed per se until Moslem times, even though there were some Roman-era riots in Alexandria in which stuff got burned down and burned up.
OK. So there was a Roman invasion in which Julius was the leader that resulted in the burning of the library. He later contended that his guys didn’t do it, maybe, maybe not. But he was there when it happened and he was leading the invading force. It may have been a bibliophobic Alexandrian that used the opportunity to destroy the library. I guess we’ll never know.