Do you have any idea as to why an animal may have been graded docked as a Bull? (Other than by mistake)?

They may be docked because of head size. The heavier the animal the larger the head. The head may have not had enough time to shrink.

Belly hair may trick them into thinking it is a Bull. Trim belly hair before sending to market.

Castrating to late, which results in an animal being to masculine and not having enough time to grain to allow marbling.

Ask the individuals in charge. They may have different grading procedures.