Sorry I'm late!
Grossberger has it: Robert's Rules section 3, irregularities, rule 15 (http://www.homepokertourney.com/roberts-rules-of-poker.htm#IRREGULARITIES):
15. If the dealer prematurely deals any cards before the betting is complete, those cards will not play, even if a player who has not acted decides to fold.
In your case betting definitely wasn't complete so the card shouldn't play. And Grossberger again has it right, you fix the error as follows, per Robert's Rules section 5, hold 'em, rule 8 (http://www.homepokertourney.com/roberts-rules-of-poker.htm#SECTION_5_-_HOLDEM)
8. A dealing error for the fourth boardcard is rectified in a manner to least influence the identity of the boardcards that would have been used without the error. The dealer burns and deals what would have been the fifth card in the fourth card’s place. After this round of betting, the dealer reshuffles the deck, including the card that was taken out of play, but not including the burncards or discards. The dealer then cuts the deck and deals the final card without burning a card. If the fifth card is turned up prematurely, the deck is reshuffled and dealt in the same manner.
So the dealer takes the turn card off the board, leaves the burn card where it is, completes the flop betting round (ensuring that everybody knows the seven will not
be the turn card but it's possible
it could be the river card), burns again and uses the next card as the turn, completes that betting round, then puts the prematurely exposed seven back in the deck stub, reshuffles and deals the river without burning.
FWIW we discussed it in the other thread and Grossberger and I disagree on the not burning a card issue: I believe it has the least possible impact on the shape of the final board because four of the five board cards and all three of the burn cards are the ones that would've been there without the error.
But I digress - and obviously this is just the technical rule in one rule book (albeit the most commonly used one). The way the TD chooses to handle any given situation is, of course, completely up to them no matter how awful I think their decision was