Selahattin Demirtaş supported him in the elections.
Even if he didn't tho, most kurds would still vote for kılıçdaroğlu because they don't like Erdoğan too. Hovewer, most don't really care as they don't like both Kılıçdaroğlu and Erdoğan, which is why turnout was low in those areas.
Basically, they hate Erdoğan more, but they don't love Kılıçdaroğlu either. They also don't care enough which is why their turnout rates dropped after the MP vote.
Kılıçdaroğlu isn't a nationalist, he just pretented to be after his campaign failed in the first round. He pretended to be a hardcore nationalist to get some more votes from nationalist people that voted for Sinan Oğan.
Ironically, he would have gotten more votes if he just pretended to be neutral on the topic.
It used to be. There is nothing nationalistic about that party anymore. They are kicking the nationalist ones left and right, like a mayor called Tanju Özcan who was actually well-liked.