Maybe Blizzard didn’t say anything about it being LFR, but the achievement mentioned “Any difficulty” and the achievement was in game for weeks with that description, that´s why i created this thread on July 17
because a lot of player tough it was available from LFR + as a participation reward, similar to the Deathwing mount from the LFR anniversary event. As mentioned by Maizou and others, the text of the achievement was changed days before the S4 launch.