I don't get it, why were the Stromgardians racist against dwarves of all races?

If you think about it, they are the very definition of a model minority.
>shares the same religion
>is well behaved, doesn't have a reputation of stealing or anything like that
>tends to keep their promises
>contributes to the kingdom through their high quality crafts and tech
>keeps to themselves, but not to the point of making a parallel society
>will actually fight alongside you during wartime(very important)
(Dark Iron niggers are obviously the exception to these)