Maybe all the others are wrong lol.
Glad to hear you have rescued him, but not sure how you have got the pedigree if he is rescued. There are lots of Westie breeders who do not bother about 'breed standards' so breed from any dog whether or not it is a good specimen.
This is what breed standards are for, so breeders have a 'blue print' to work towards, rather like the instructions with an airfix kit, without the instructions your plane might have its wings in the wrong place! Unless breeders choose good specimens to breed from and use a good dog, the pups can look very different from what they are supposed to. This can happen in any breed, but more so in the common breeds. I saw a Cavalier the other day that was as big as a Springer Spaniel, but the owners assured me he was 'Champion bred' whatever that means. Its even worse if dogs do not have papers, they can use what they like and say they are what they like!
All I would say is love him to bits and don't worry what he looks like. If you give us his Pedigree name and date of birth I will make enquiries about the breeding for you.