Pokémon X and Pokémon Y

And how did he "only" see the pokedex entry of the mirror pokemon, as well as the fact it has an evo, yet not know the evo's name?

Could be more than one person working for the website, and someone else got the review copy and he/she is just being nosey.

I'd be pretty sure anyone who did get a review copy wouldn't blurt out secrets because of NDAs they probably had to agree to.

So it's not impossible, but yeah, I agree, they're probably making it up.