North Dakota House districts 2, 14, 15

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The The 2016 North Dakota Democratic caucuses were held on June 7, 2016.
Bernie won them with 64.21% of the vote, Hillary received 25.63%, and 10.15% of the voters were uncommitted.
Unlike all the other primaries and caucuses states (except Alaska), the North Dakota SoS doesn't deliver county results, but House district results. Here I noticed something strange: In the House districts 2, 14, 15, neither Bernie nor Hillary won a plurality; most of the voters were uncommitted.
How is this possible? You have to show up personally and have to publicly declare that you dislike both candidates - even though the primary season was almost over and it had already been clear who the nominee would be.
What kind of Democrats live in those districts?
The most populous city in HD 1 is Stanley, Mountrail County; in HD 14, Rugby, Pierce County, has the most citizens; Devils Lake, Ramsey County, is the biggest city in HD 15.



While we're at it: Why did the Democrats living in the House districts 23 (New Rockford, Eddy Ct.) and 33 (Beulah, Mercer Ct.) vote for Hillary?

[Dr. MB]

I’d just guess dissatisfaction with the establishment, registered Dems who are effectively Republicans, and very low turnout in those areas.