Appeal granted in accessory use case

In the case of Capelle v. Orange County, the Virginia Supreme Court has granted the petition for appeal on the following issue:

"The Orange County Board of Supervisors, without legal authority and in violation of Virginia law and local zoning ordinances, illegally burdened a designated limited residential zoning district with mining and trucking uses of an adjacent agricultural zone by accepting, as an accessory use, the use of a private road through such limited residential district to serve the mining truck hauling uses of the agriculturally zoned parcel."

Ah, now, I thought an accessory use typically would be a use that is otherwise unlawful but for its character as accessory to a lawful use - if it has to be a lawful use in the first place, then what difference does it make whether it is "accessory" to another lawful use?