Probably an explanation why dwarves appear Scottish is that dwarves are beings from Norse mythology and folklore that come up as creatures called trows in Scottish folklore.
Quote from wiki:
In the folkloric traditions of the Orkney and Shetland islands
(Scotland), a trow (alternatively trowe or drow) is a small,
troll-like fairy creature. Trows, in general, are inclined to be short
of stature, ugly and both shy and mischievous in nature. Like the
troll of Scandinavian legend, with which the trow shares many
similarities, trows are nocturnal creatures; venturing out of their
'trowie knowes' (earthen mound dwellings) solely in the evening, they
often enter households as the inhabitants sleep. Trows traditionally
have a fondness for music, and folktales tell of their habit of
kidnapping musicians or luring them to their dens.
Trolls are mentioned here, so I just wanted to add:
Quote from wiki:
In later Scandinavian folklore, other kinds of nature spirits
(Vættir), like the Troll and the Nisse, take over many of the
functions of the Dvergar (dverg - Norse/Norwegian for dwarf).
Many of the important dwarves in Middle-earth got their names from significant dwarfs in Norse mythology.
Quote from wiki:
In Tolkien's Middle-earth, Durin the Deathless, a character based on
the Norse figure, is one of the founding fathers of the Dwarves.
Quote from wiki:
In Norse mythology, Dvalin is a dwarf who appears in several Old Norse
tales and kennings. J. R. R. Tolkien took the name as Dwalin for one
of the dwarves in The Hobbit.
Apart from this and all these great answers, I just want to add some other similarities:
- Beard (they have impressive beards)
- Fighting on foot, as opposed to fighting on horseback
- Kilt (some dwarfs have been seen wearing one, and dwarf women prefer wearing one)
- Similar weapons & siege engines
- Skin and hair/beard color (which is similar to all northern people)