First, let me say I don't think it was a touchdown.
Now, the line judge thought it was. That's a pretty tough call for him to make so I see little fault with his decision as it was close and hard to see for sure in live action.
As far as the replay goes, the rule is, the referee has to see "Irrefutable evidence" that the call on the field was wrong if he is to overturn the ruling. When I watched the replay, I could not see the ball just before Ben was down. I could, however, make a reasonable estimate of where that ball was in his arm and where the ball
should have been when he was down. The tip of the ball
should have been over the line. In order for that referee to reverse the call, he actually would have had to
see the ball
not cross the line.
As a referee who only overrides the field call 23% of the time, I think he made the call in character. In a techical sense, I think he made the right call. The problem really lies with the initial call on the field which is a lot tougher to make in the moment.
Aidan thought the call was BS: