I heard a rumor that the amount being released is closer to 350K and they are giving lower numbers so they don't scare people, and so they won't be blamed/sued for flood damage.
I know you said rumor, but I think that's a bit far-fetched. First, they'd have a bigger suit (were one even possible) for misrepresenting the data. Second, I think they're immune from any liability in the first place being a government entity in the capacity they exist.