Also found this:
CAMPBELTON, (or Campbelltown), a village in the parishes of Ardersier and Petty, in the county of Inverness, 10 miles to the N.E. of Inverness. It is seated on the coast of the Moray Firth, not far from Fort George. The Earl of Cawdor, from whose family name the village is named, owned the land on which the village is built. That part of the village in the parish of Petty is sometimes called Stuarton. Here is an United Presbyterian church, and on a neighbouring eminence the remains of a British fort, Here is also a chalybeate spring, and the village is frequented as a watering-place."
So Angus Sinclair was likely from Campbeltown in Petty, not Argyllshire.