The main finding may indeed be true, but there is no mention of whether the researchers tryied to control for the length of stay in an apartment. It's quite likely that the average foreigner may have resided in his/her current residence for less time than the average Swiss person. It is my understanding that rent increases are more likely to affect new residents and not current residents, because current residents may already be tied into a certain lower rent level for a certain amount of time, and landlords often only change the rent when new residents arrive.
Therefore, it is possible that all or part of the effect that the research documented can be explained by the length of stay in the current apartment being longer for Swiss people than for non-Swiss and if this is true then discrimination is not a factor. I'd like to check whether the researchers controlled for this in their analysis, but the swissinfo article is not informative enough to give this essential information, and unfortunately the abstract of the original article is not even available on the
publishing journal's own website, I assume because the actual article hasn't officially been published quite yet.