Congrats! The neat thing is that you have the proof right there in the game, because the ball used is shown when you send it out.

It'd be less of an acheivement if you had deliberately gone out to do it with dozens of pokéballs, but the fact that you fluked it as a last ditch effort makes it special

You'll be able to casually pooh-pooh all those Master-, Timer- and Dive- ball caught Kyogres. Don't let your 00berness go to your head!

(Of course, if you'd actually caught it with a Safari Ball.... damn, I'd be impressed!)

In theory you could get it with a Nest Ball for novelty, or a Luxury Ball because you REALLY care about your pokémon...