The contract that had to move was Walman, not Gibson. The claim is that 1) there are pending moves that required additional cap space, 2) Walman was the roster player chosen to deal in order to provide said cap space, 3) an additional draft pick was needed to deal Walman, and 4) swapping Gibson for Kiiskinen (who they rank equally) provided an additional pick.
Now I'm not saying I agree with all of those claims - particularly number 3 - but that's the scenario.
Ultimately this all depends on what the pending moves are. If Detroit lands Stamkos and Roy, the kids look good, and they make the playoffs, nobody will care about Jake Walman or the second rounder or Gibson. But if they strike out in free agency, make no significant trades, and use the money to bring back Ghost, it's going to be a lot of egg on Yzerman's face.