Hello~
Yes, that is a Westie...does not looked mixed. I owned a Westie and actually raised one litter of her puppies. Your little guy is a Westie (maybe not the best bred, but he is a cutie-pie.). At that age, Westies tend to go through a very akward stage...atleast ours did and so did her puppies. Once he starts to fill out and his fur comes in more, he will start to take on more of the Westie look. However, if he was not well-bred, he might not ever have a great coat on him....won't change how incredibly he is, thogh.
I just love Westies, ENERGY ENERGY ENERGY!
Hope this helped some~
Tammy