Henry George Liddell, Robert Scott, A Greek-English Lexicon, κῆπος
I've always taken it that he simply taught in his garden. Just like the Plato's Academy was in the gymnasium named for the Athenian hero, Akademos. Outside the city walls of Athens, the gymnasium was made famous by Plato as a center of learning.
Lyceum is a Latin rendering of the Ancient Greek Λύκειον (lykeion), the name of a gymnasium in Classical Athens dedicated to Apollo Lyceus. This original lyceum is remembered as the location of the peripatetic school of Aristotle.
The stoics were named for the Stoa Poikile, the Painted Stoa, the public arcade in the Agora.
So, it was very common to name the school of philosophy for there they met. Epicurus was somewhat unique I understand because he taught on his own private property - his garden - and not in a public setting.
PS. I should add that some of those descriptions above are cut and pasted from Wikipedia. It was easier to do than composing info about the lyceum and academy.