Property Damage Liability Coverage Dispute

Our insured is in the tree service and stump grinding business. After completing a stump grinding job, the insured was loading the grinder onto his owned trailer that was attached to his business truck The grinder was half-way on the trailer and part-way out in the street when a vehicle came along and struck the grinder. The damage amounted to $2,000 to the vehicle.

The insured has a general liability policy and a business auto policy. If the insured is held liable for the property damage claim, would this be covered by the business auto policy or the general liability policy?