Presuming it came over the GTS, I'd say it's legit enough (given Nintendo has its checks in place for that).

I caught my first Gen 5 Shiny not too long ago in White, a Shiny Seedot caught in White Forest. Hoping to see more of them, given I have a few Shinies from Gen 4 (Gloom and Donphan in HG, Geodude and Vulpix in SS, and Pichu in Plat) plus the Red Gyarados (actually, two of them).

I wonder what the Shiny Charm will do for collecting Shinies, given that I doubt it's an item that's going away (though they probably could make it not as annoying to get as it was in B2/W2).