Uhh, I don't know! I don't know where he came from, but... someone said he came down from the mountains? Snorlax just really love food, so he was probably attracted to the city that way? But I don't know which mountains he came from either...

[ Maybe he should have asked Snorlax this when he was a pokémon. Alas! ]

But I doubt a pokémon like a snorlax would live anywhere without food, you know?