I think it is the intent to provide sprinklers in accessory use areas if they are a part of and serving the A5 occupancy regardless of how remote since there is no language in the code section addressing that. I believe more information is needed for this situation particularly to determine if this is Open Mall.
Yes, IF part of an actual structure. (bleachers, stadiums, grandstands) An individual stand alone restroom building, may be incidental to the use of the space, but it is not inclusive to a A5 structure.
***So maybe the response should be, No, in an open plaza area???????
Agree with Michael. If the accessory use is to serve the A5 occupancy, fire sprinklers are required for the accessory use. (I am going on the assumption that this has been properly classified as an A-5 occupancy.)