Hi Ew:
Very interesting indeed.
As a preliminary note, although it is too late to correct by the time you get to the table, IMO dealers must be made aware of the general principle that the mere action of turning cards face-up is NOT considered a fold. There are many situations in which it would appear that a player's intention is to fold, but one should not assume. In my view, it is very important that once Player A opens his hand, the dealer should have asked A to confirm that he intends to fold before allowing any further action to continue. The answer to the dealer's question of "Are you folding?" will be "Yes" most of the time, and in response, the dealer should muck the hand immediately. Player B then can show if he wants. Dealers will feel pained to ask players to explicitly confirm that they intend to fold after a hand is exposed, when it is probably true 99% of the time, but it will save a lot of headache for that 1% of the time in which it actually becomes an issue.
Strictly speaking, exposing one's hand is not a binding fold, in the absence of a verbal declaration. Since the cards are not irretrievably in the muck, they are live. We no longer kill a hand simply because the cards are exposed. A penalty can be imposed at the end of the hand per Rule 53. If one were to award the pot to Player A, he should definitely be getting a HUGE penalty here -- perhaps at least 3 rounds if not more.
However, I am more inclined to agree with the "second" group's observations that the player's actions were highly unethical, and a blatant angle. I should note that Player B could have protected his hand and himself here by asking the dealer to confirm that A has indeed folded before flipping over his hand. However, this seems like a prime example for applying Rule 1 here and awarding the pot to Player B in this particular situation. And yes, I would definitely still give Player A at least a one round penalty on top of that.
In summary, although I think I'd have to be there to get a feel for how blatant the angle was by Player A, I would lean towards awarding Player B the pot based on how it has been described. It might even be possible to justify this without having to apply Rule 1... Note that Player A did not simply expose his hand here to get a reaction from B, A explicitly announced "If I FOLD and show you my hand"... Can we not say that is a declaration of fold? If he didn't intend to fold, he definitely shouldn't say the word "fold" and then release his hand, and it's up to A to ensure that his intentions are clear. I am not going to play grammarian, and argue over the "if". If Player B could have reasonably interpreted this statement as "I am folding and will show you my hand. Will you show me yours?", then I am interpreting that statement as a fold once the cards are exposed, and only A is to blame.