This is not quite correct, but I'll admit, the rule is a bit unclear. As I understand it, you can challenge a spot if the challenge relates to whether you got a first down, or if it involves the goal line. Sometimes a challenge may be unsuccessful--when review shows that the ball was short of the first down marker--which causes the challenging team to lose a timeout, but the ball is nonetheless re-spotted because the original spot was wrong.
Here I suppose McDermott could have challenged on the basis that Allen scored a TD on the run...the challenge would not have "succeeded" because he clearly didn't cross the goal line, but the replay would have potentially resulted in a correct spot. At that point, we had plenty of timeouts so "losing" the challenge would not have mattered.