Oh yeah, I saw that a while ago. While at first I wasn't 100% sure if it was an OVA or some random event, I then found out that it was drawn by some doujin circle named Singerly or something. They are known for their eerily well done K-ON art. But yeah, you can tell it's not KyoAni's style because it's lacking the bold moeness.
<---- Slave for K-ON. Absolute slave for it.
Edit: It's actually evident on the bottom of the picture that the illustration was done by Ingerly. The original illustrations are done by Horiguchi and I doubt they would really replace his God-like artwork with some doujin maker's artwork.
"Just tell me why, baby, they might call me crazy for saying I fight until there is no more"
-- ONE OK ROCK, Taka (The Beginning)