The following is based on personal speculation so, once again, feel free to correct me if I get this wrong.

 While there are some surface similarities between racial hygiene and ethnic cleansing, I believe that the concept of racial hygiene did not play a major role in the expulsions documented in this article.

 The major unique feature of racial hygiene is the concept of race and genetics (eugenics).  This concept argues that you are who you are by dint of your parents race and genetics and that what you think and how you act is irrelevant to the "pollution" caused by your inferior genes.  Thus, Hitler could argue for an Aryan super-race that was polluted by Jewish, Slavic and other inferior races.  If you had any forebears from a non-Aryan race, you were suspect.

 In contrast, ethnic cleansing is more about removing those of a different ethnicity where ethnicity is usually marked by language, religion and customs.  Those considered to be a different ethnicity might be of the same race (e.g. Hutus and Tutsis in Rwanda).  It is hard to argue that Poles and Germans are of different races unless you are a Nazi.  To most people, they are just different ethnicities of the Caucasian race.  It is similarly hard to argue that the various ethnic groups (Serbs, Croats, Bosnians) in the the former Yugoslavia are of different races.  As far as I know, the major differences are language and religion.

 As a thought experiment, consider the case of a German woman married to a Polish man in the first half of the 20th century.  If the family spoke Polish at home and raised their children as Poles (i.e. Polish-speaking Catholics), would that family have been expelled?  I doubt it.  If you agree, then you can see that the expulsions of ethnic Germans may have been motivated by ethnic cleansing but not by racial hygiene.

 Hope that helps.