I
believe this is being misquoted, and it is actually one of their new "Challenges" - time based objectives, that don't carry Gamerscore.
http://majornelson.com/2013/06/12/xb...-achievements/
EDIT: Important text from article below: (emphasis mine)
There are now
two types of Achievements: achievements and challenges. An achievement is probably already familiar. There’s a goal or activity you must accomplish and a reward that you receive upon completion. You can unlock an achievement at any time, be it on a game’s launch day or 3 years later. I guess you can say an achievement is like a promise in that sense.
A challenge, on the other hand, is more like an opportunity – better grab it while you can! It is also comprised of a goal and a reward; however, challenges are time-bound (as in, real life time). That means you can only unlock during its eligible time window, and if you get close but don’t complete the goal when it ends… *Kanye shrug*
Achievements and challenges are both officially considered Xbox Live Achievements