It's a quirk of the Romance languages, which Esperanto is heavily based upon. It works the same in Spanish and Italian.
In Spanish: conocer - conocido
In Italian: conoscere - conosciuto
In Esperanto: koni - konata/konita
In all of these languages, the participle form for the verb "to know, to be familiar with" can either mean literally "known" or more colloquially as "well known" in reference to fame or notoriety.