No it is not true. Highland dress as we know it today owes much to the military. Initially, the army very much followed the civilian dress of the day and adapted it to military purposes, but after the Proscription, the opposite became the case and civilian dress followed that of the military. Such characteristic features as the shoulder straps on today’s jackets and the buttons on the sleeve are of military origin. The cuts of various forms of evening jacket can also be traced back to the late 1700s. The plaid became a separate garment and survives in military uniform today in two forms, the fly plaid, a vestigial piece of tartan draped from the left shoulder, usually worn by drummers, and the full shoulder plaid worn by pipers and bandsmen. The plaid is still carried as a length of tartan over the shoulder in civilian dress.
Wear the plaid!