Hi,
I think I would agree with Forfarian. I did a bit of noodling and the firm seems to have been set up by brothers James and Patrick, sons of a farmer from Renfrewshire. As Forfarian suggests moving around like that seems unlikely, especially as a proposed son of an established business.
The only suggestion that I can see that might be plausible would be an even earlier link, and I think only DNA would solve that one.
That being said there were links between deepest Aberdeenshire and Lesmahagow in the 1850’s as attested by my own family.
There are also Clarks with deep roots in the Ballater area, so you don’t have to go too far to find possible ancestors of Robert.