First card dealt? Or first to those players?
Well, even if it was the first card dealt, if you rule it as exposed, a re-deal is proper. Rule 35-A-6.
But i assume you meant first to that player. I don't think it changes anything.
The exposed card rule is intended for occasions when a card is exposed by the dealer, either thru clumsy handling, or catching a corner on the felt, or hitting something, etc. I.E. The card has become exposed due to unfortunate circumstances, but not due to a player's mishandling of the card. Once a card has landed and settled unexposed, if a player later exposes the card, they have to live with it.
The word 'misdeal' means a mistake when dealing, which is what happened, even though the mistake was made by the player. This situation is more consistent with a player getting an extra card. And technically, that's exactly what happened. He was holding a card that did not belong to him. If the error wasn't discovered, he'd end up with an extra card.
And since the extra card was discovered before significant action, it's a misdeal.