Obviously. "Another" Esbern
There are lots of people in real life who share the same name, there's no reason why there can't be in the Elder Scrolls as well, in fact, I'm pretty sure there are a number of names that have been used in the series multiple times for different characters, Cyrus, for example, I seem to recall a Blade named Cyrus in Oblivion, and Cyrus is also the protagonist of Redguard.
I think we can assume the Esbern in Skyrim is not the same Esbern as in Knights of the Nine, as I'm pretty sure Nords don't normally live for over 200 years, but it could still be that there's an intentional reference here, not that they're the same person, but just that Bethesda thought it would be a clever refence to a previous game to have a character in it share a name with another character.