Broken RNG: 3 "cat" music discs in one dungeon chest

I started a survival map and found a dungeon in a ravine. In the chest were 3 "cat" music discs. I wouldn't have posted this except the odds of 1 disc showing up in a single chest are 1/120, based on http://www.minecraftwiki.net/wiki/Dungeon, So is this a bug or am I just that lucky.