Handball by the keeper outside the box is a red card.
That's not correct. The law does not say that handball outside the penalty area = a red card for the keeper. The law says that "denying the opposing team a goal or an obvious goalscoring opportunity by deliberately handling the ball (this does not apply to a goalkeeper within his own penalty area)"
Link at:
http://www.thefa.com/football-rules-governance/laws/football-11-11/law-12---fouls-and-misconduct.aspx#xdD2R59ERUmtzp1Z.99The question being asked is whether the York keeper could have been shown a red card despite Hackett scoring, and the goal allowed to stand with play resuming via a kick off.