From GTS. It says: KANTO - Apparently arrived after a long travel trought time. Does it mean that he's from III gen?
Yes, it does mean that it's from Generation III. It has been through 2 migrations, so it has been on a long journey.
Probablly, But pokemon logic is weird so it could be lots of things.
Maybe - like pokemon said, Pokemon logic is very odd so it could mean a lot of things. But the best thing to do is to ignore it, really. Thinking about it will most likely make your brain hurt.