Edit: It looks like this study is just self-reporting on how people feel about different breeds?

It is, but the statement I cited is not a conclusion of this study but a reason why the study was conducted. The study itself wants to learn how strong the bias is that leads to these stereotypes, because one of the issues of gathering data is bias. Basically, people buy certain breeds expecting a certain behavior and then train these breeds to express said behavior, which makes it difficult to examine whether said behavior is due to the nature or nurtured or how big a role either plays.