Kelvin,
You have not missed anything!. You are absolutely right. However, I still maintain that the so called experienced official reverted back to an older recognized mechanic for some reason and it does help out the lead to a certain extent as the floor is more balanced and the lead only has to concentrate on what he's looking at and not worry about the sideline to his left etc.
I actually think the lead appreciated the move in this case and I would love to hear what the trail has to say re: why he did it. We must not be too quick to criticize. Mechanics change all the time over the years - they often revert back and forth as you will see it if you stick around long enough. Also,remember there is never a magic spot on the floor, we are always trying to anticipate what is going to happen and get into the best spot to observe that anticipated action. I believe that's what the trail was doing in this case. If I was in the stands evaluating these guys during this game I would certainly have noted this move and questioned it. If the trail answered with a good explanation I would have no problem but would remind them that it's not a mechanic that's generally taught and should be used with caution and gone over at the Pre-Game.
Pistol

THERE YOU GO!!!
 

I think Richard has said it all. In his situation he would have really appreciated it if he and his partner had discussed this situation at Pre-Game and had his Trail in that case cross over to cover the weak side baseline.
Anticipation is always the key to good movement.
Pistol