Dc Dc regulator malfunction
That very well could have been what happened.  This can be a problem with internal switch regulators in that you may have had a shoot-through event, a time where both of the internal mosfets were activated, and current shot straight from your VIN to PGND.  This would cause massive current flow and could damage the internal components of the IC.  I don't see any mention of shoot-through event protection on the datasheet.

If you are running this all the time, then this may not be the best regulator for your application, I note a piece in regards to the Over-current protection:


  However, the IC should
  not be used in applications characterized by continuous
  operation