I suspect it was a touchdown but they didn't have the needed angle to overturn it. I question if the goal line official on the right side could actually see the ball. The ball carrier rolled to his right as he was tackled and I think his body shielded the ball from that official. The official could clearly see the knee go down short of the goal, but I suspect the ball crossed the plane simultaneously(but only just). But without a goal line camera angle from the left side, there's no way to know for certain.
Wally the Bronco doing some fine YouTube thumbnail work