I'm not sure I love the floor's ruling here either, but this situation is so weird, who knows what's right.
If the floor has determined that substantial action has applied, then I think they have to make some effort to determine who had the last live hand. Even though the BB is the villain in this situation, she's technically right, hero's hand is dead the moment she screwed it so I just don't see how hero can win the pot. Assuming everyone more or less folded in order, and knowing yours and the BB hand's were dead the moment she screwed up, I would be inclined to award the blinds to the button by default.
That said, the floor's assumption that substantial action applies feels flawed if the error was discovered before anyone actually acted, so I am inclined to think misdeal is the best call and I would apply a one-hand penalty to the BB. Not substantial, but enough to lay the baseline to deter repeat offenses.
(Edit to add: if I were to speculate, the floor may not have done this one by the book, but took the opportunity to teach the lesson, always hold your hands until the house confirms a misdeal and to further teach the lesson, don't grab the neighbors cards. In other words, the floor found that hero is the least to blame for the situation and awarded the pot accordingly. Though I do think this ruling overlooks hero's responsibility for protecting his hand when dealt.)