yeah, that was the thing that concerned me. I don't know the 100% sure source of information, if there were even shiny MYSTRY mews. That goes as well to shiny Metang. They may be hacks - that's because I have written "can't verify it's legitimacy, sorry :(".
Anyway, event pokemons aren't always the same. They sometimes differ with natures, IV's and stats - I have a few different 10JAHRE pokemons... Dunno what to think about it.