That I do not know about, technically you don't want any dead root material, but it happens a lot even outdoors, so I would not have bothered to cut it off if it was my plant.
Because the lower roots go to the upper part of the plant the higher roots go to the bottom of the plant.
Your upper part of the plant was affected due to being rootbound and some of roots dying.
Because the lower roots go to the upper part of the plant the higher roots go to the bottom of the plant.
Your upper part of the plant was affected due to being rootbound and some of roots dying.