
Thing is would you know the difference if it was a cairn clipped in westie style. I don't think I know enough about the breeds differences in head to know. To me apart from the haircut there is little difference, and as the Westie was bred from the Cairn then that is not surprising.
My Guess would be it is a Cairn in a Westie trim.
Breed standards for head of the two breeds:
Cairn:
Head and Skull
Head small, but in proportion to body. Skull broad; a decided indentation between the eyes with a definite stop. Muzzle powerful, jaw strong but not long or heavy. Nose black . Head well furnished.
Westie:
Head and Skull
Skull slightly domed; when handled across forehead presents a smooth contour. Tapering very slightly from skull at level of ears to eyes. Distance from occiput to eyes slightly greater than length of foreface. Head thickly coated with hair, and carried at right angle or less, to axis of neck. Head not to be carried in extended position. Foreface gradually tapering from eye to muzzle. Distinct stop formed by heavy, bony ridges immediately above and slightly overhanging eye, and slight indentation between eyes. Foreface not dished nor falling away quickly below eyes, where it is well made up. Jaws strong and level. Nose black and fairly large, forming smooth contour with rest of muzzle. Nose not projecting forward.