He's spinning because he has nothing else. This was indefensible given the dire circumstances.
Why is it indefensible? AS I understand it, he turned back only foot traffic, not vehicles.
What should he have done? Had he allowed the "small groups" of people into Gretna, where would they have gone? Into other people's vacant homes, businesses, etc.? This would have worsened the recovery and certainly not "saved lives," since it is doubtful that any of the 30 elderly people who perished at the Superdome would have been any less uncomfortable on the other side of the bridge. Gretna had the same heat, the same lack of power and electricity, etc., and no apparent resources.
If the story is true, and Gretna is unflooded, largely undamaged and habitable, it will be a valuable location during the recovery period, when the appropriate services can be relocated there.