Question about an exposed hand ruling

[VegasRunner]

I was ruled aganist in a live game today in Vegas and I'd like to hear some other people's opinion on what I think was a poor ruling. Tell me what you think the ruling should be and I'll post the floor person's decision and what my role is in all this in a couple days.

The game being played is nine-handed $2-$5 No Limit Hold 'em.

SB-post 2
BB- post 5 (has about $500 behind)
seat 3-folds
seat 4-calls (has about $350 behind)
seat 5-fold
seat 6-calls
seat 7-fold
cutoff--raises to 25 (has about $450 behind)
button--folds
sb--folds
bb-calls
seat 4-raises to 125
seat 6-folds
cutoff-all in for $450

At this point, the Big Blind goes into the tank, debating whether or not he wants to call, but before he can make his decision, Seat 4 accidentally exposes his cards to the Big Blind. After seeing the exposed cards, the big blind immediately mucks his hand.

The player in the cutoff calls the floor over and wants Seat 4's hand to be killed for exposing his cards in a multiway pot while there is still action. Seat 4 claims that it was an honest mistake and he only exposed his cards because he thought he was in a heads up situation with the cutoff. The Cutoff doesn't care if it was an honest mistake and continues to argue that Seat 4's hand should be dead because his mistake cost the Cutoff expected value from a possible call by the big blind.

No one at the table disbutes the following facts:

1.The Cutoff's hand was much stronger preflop than the Big Blind's.
2. Seat 4's exposed cards were clearly a major part of the Big Blind's decision to muck his cards.
3. Seat 4's mistake was an honest mistake (he wasn't trying to influence someone's decision, he simply screwed up and opened his cards too quickly)
4. Seat 4 would have called the Cutoff's all-in bet regardless of the Big Blind's action.

What do you think the ruling should be?