I agree with you but I think you are a little harsh regarding the conclusions which are drawn by the authors of the paper. There are actually two types of polarisation: ideological and affective. The paper, as far as I understood it (and you seem to agree), mainly concerns itself with ideological polarisation (i.e. polarisation on policy issues). Affective polarisation on the other hand describes animosity against a certain group because members of that group are members of that group (= "identity"). The authors of the paper clearly state how to incorporate affective polarisation in their model and I am very interested whether someone actually takes up that challenge and what the outcome is.