Right, it's a normal and expected property of the exponential distribution (that distribution of interblock gaps) that there are a lot of small values; more than you'd probably expect after being told there was a 10 minute average. E.g. about 10% of blocks are 1minute or less apart (assuming lambda=1/600; in reality because of hashrate increases the expected time is often more like 8 minutes). Other constraints like the minimum value for the time coded in blocks also contribute to making the timestamps have less diversity than you might expect from a first guess.

In the case here, they're not even unusually closely timed the times on the four blocks in question are 12:24 13:02 13:12 13:11 (the prior one was 12:03).  Note that the times aren't monotonic, which highlights a previously mentioned limitation in trying to reason about time; they're not all drawing from the same clock as there is no singular now in a decentralized system.

I personally observed these blocks at the following times:

2015-05-02 12:25:21 UpdateTip: new best=00000000000000000f8d7a12d307ddc717cab90d2ced5c7320624a13714b0aa3  height=354640  log2_work=82.71737  tx=67422028  date=2015-05-02 12:24:26 progress=0.999999  cache=14812
2015-05-02 13:01:37 UpdateTip: new best=00000000000000000a1ebf23947c2dc38f980c66c1fd1303235326e36ea5afae  height=354641  log2_work=82.717407  tx=67424094  date=2015-05-02 13:02:15 progress=1.000001  cache=9138
2015-05-02 13:05:29 UpdateTip: new best=00000000000000000f181b8cfb70624cd74bcac01c930657bd1bde85ff59e7fd  height=354642  log2_work=82.717444  tx=67424677  date=2015-05-02 13:12:17 progress=1.000007  cache=10305
2015-05-02 13:08:46 UpdateTip: new best=000000000000000015c33a22604bd9c01806c3add1b33d6b8dd1e663da95cbd1  height=354643  log2_work=82.717481  tx=67425354  date=2015-05-02 13:11:28 progress=1.000003  cache=11807


So gaps of 36:16, 3:52, 3:17.   Given a ~10 minute expected time about a third of blocks are 3:17 apart or less.