Fergus I kilted image from 1792

[M. A. C. Newsome]

It is very hard to make conclusions with such a small rendering of the image, I am afraid. But this could very well be an attempt to depict the belted plaid (or feilidh-mor). There are other depictions of the feilidh-mor fastened at the front of the breast in this manner. For example, this painting of Duncan Campbell of Lochow from 1635.


I also think it rather more likely the artist would attempt to portray King Fergus in the feilidh-mor for, as you say, the tailored kilt was still rather a new fashion in the 1790s and it would be unlikely (to my mind) that the artist would depict this ancient king in a style of garment that would be recognized as something very new. Whereas the older feilidh was still being worn and would also be familiar with many as an older, more traditional kilted garment -- and therefore more proper to depict on an ancient king.