Telvanni towers can be naned after the wizard that grew them - like Tel Fyr - or after the location they're grown on, like Tel Uvirith or Tel Vos. Most likely the wizard that created it was called Galen (sounds enough like a Dunmeri name), or the location was called that before the tower was built.
As for the actual meaning or relation, we can only guess. Firesong might reveal something about the origin, if we're lucky!
There are Dunmer with the last name Galen so that’s probably what happened. I hope the connection is revealed at some point since I don’t understand how an elf from the opposite side of Tamriel and a breton island could share a name unless it has some connection to the Aldmer.
Edit: Galenwe also has Galen in it… so maybe there IS an Aldmer connection somewhere?