Likely it's an indication of decreased difficulty and hashing power in the bitcoin network. It could be a fluke of chance that will be made up with a 1 second block. I don't know the specifics.

Generally, if hashing power increases drastically you will have blocks resolved under 10 minutes and the network adjusts the difficulty upwards. If hashing power decreases, you'll see blocks like this.

Let's see if someone with knowledge of the source code has a better answer.