I suspect it's due to an accident. There might was something wrong with the mempool of the pool's node at that moment and during the in-between period they were trying to find out what's wrong, one of their miners solved the block.
nope. not an error
when a pool makes a blocksolve it knows it has a bit of time to quickly work on another block while the network is propagating its first block. so instead of wasting time collating transactions to make a new blockheader it just begins a 'empty block' and as the asics run through the first few rounds of their nonce/extranonce. the pool then starts adding transactions into a blocktemplate for the next header to send in the next round of hashing once then finished their attempts.
you notice this happening most when an empty block is solved within 3 minutes of the same pool solving their previous block... AS IS THE CASE WITH THIS TOPICS BLOCK NUMBER