I would say, most likely. Even though you did not provide the level or nature, the high stats and Pokérus should be a big giveaway. Another way to verify would be it's IVs. Use the 'Judge' feature, which you can get after hatching 20 eggs and talking to a man in blue at the Battle Tree, and see if it has abnormally high IVs. If it does, I would say 100% chance it was hacked. If not, perhaps you just got lucky.
For the most part, shiny Pokémon off Wonder Trade are hacked. But if it doesn't seem to be anything special IV wise, there is a good chance that it is legit.
I'm no expert, but this is, I believe, a good way to find out if your shiny is legitimate or not. I hope I could help! ~ Artsy Ampharos
