Not necessarily, but let's look at it this way. There's not actually a lot of people with the games - otherwise you are assuming that most stores in thouse countries released early by ten days. Then a bunch of people wouldn't even be leaking to avoid any possible issues in doing so.
Then there's the shiny rate chance (1/8192 - very unlikely this changed), and for the guy to have already done enough to have trained his Charmander up to a Charizard and gotten the mega stone item for it, assuming it's even available in-game at an early-enough stage. And only wanted to share that one image, based on the possibility there's an alternate Y form which came up after not-yet-confirmed info from a different leaker.
What I'm saying is that there's already a lot of ifs and buts there. =p Without proof they really have the game (like how we know the instagram guy has it - he posted images of the card and a lot of other images), it was a long shot even before you factor in the fact it's a shiny. We've seen a lot of fakes as it is.