at a quick glance I still don't find Ardersier suggested as an alternative when searching for Campbelltown there, or vice versa.
Well, it isn't an alternative. Campbelltown is only part of Ardersier, so they are not strictly alternatives. If you search for Campbelltown, then go to Inverness-shire OS Name Books, then to Volume 08, you will see that the page header says 'Parish of Ardersier'. Volume 55 is for the parish of Petty next door, and contains references to Campbelltown. The Name Books list names of places; they don't offer alternatives.
Also, your sound advice to confirm the Parish and County when searching place names gets me wondering - the birthplace of "my" Alexander Grant in the 1851 Census* looks rather like "Campbeton pa", which I took to mean possibly "Campbelltown parish" - BUT from what you say, Campbelltown was the name of the village ONLY , it was not the parish name. The parish was Ardersier. Am I going mad?!
No, not at all.
I looked at the transcription on
https://www.freecen.org.uk/cgi/search.pl and note that it says Alexander Grant was born in Argyllshire, Campbelltown. I suspect some assumptions or guesswork by the transcriber, which is disappointing because normally I would expect FreeCen to transcribe what is there, not what the transcriber thinks ought to be there.
Having taken a look at the original, I am trying hard not to read the last part of it as 'In' rather than 'Pa'.