Part way through the 2nd quarter, the Umpire found himself caught between two Dolphin defenders, and was knocked to the ground, and got a bloody nose, or a cut lip. He was down for a few moments, and then was tended to by the Dolphins trainers. He left the field, and did not return. If I were to make a totally non-medical guess, I would think he might have required some stitches and he might have had a concussion.
In any event, the NFL has 7 officials work the game. They are arranged around the field so they can see most of the action, line play, etc, and still manage to keep track of time as well as down/distance. The rule says that they should use their best judgement to re-arrange when there is an injury. And in this case, they had the back judge move to umpire. He still had to perform some portion of the back judge duties, but he also shared some of them with the other officials. But that often means that certain plays that might otherwise be called may not be, or they might be called incorrectly, because there's one fewer set of eyes watching the play.
As an example, take the play where Bess was running an out pattern, and a flag came in for pass interference. The crowd cheered, only to learn it was on the offense. The replay they showed made it pretty clear that Bess never touched the defender, and the defender knocked Bess down before the ball got there.
What went wrong? Typically, the back judge would be the arbiter in such a situation. The linesman may have seen seapration, but not how it happened, and ASSUMED it was offensive intereference. And the back judge may have had a better angle and said it was actually okay, but the defense committed the infraction. In this case, the back judge was closer to the line filling in for the umpire and never saw it. So what the linesman thought they saw might not have been the case.
...and that's the kind of thing that sometimes happen when an official goes down to injury.