I read somewhere that the traps where known to close accidently. I think this is the part that is left out in all recent publications.

OK I found some:
It's still not known what caused the doors of the cage traps to close. They have been known to shut inadvertently, but Brian Gorman, a spokesman for the fisheries service, said it's unlikely the doors of two cages would accidentally close at the same time

http://www.latimes.com/news/nationworld/nation/la-na-sealions15-2008may16,0,6588276.story

He is denying that they closed at the same time? Who said they did. One closed 12 hours after the first!