I have seen this outside Shock Gauntlet and I think it has something to do with the Daemonhost’s aggro calculation not resetting and hitting trigger point even when players are no longer in proximity. Its pretty rare but very scary.
It does look like it. Plus you can see the soulblaze aura around it afterwards (from the Wrack and Ruin feat), which maybe means the DOTs aggro’d it a second time? It’s happened to me before =P