The original quote was "Northern states are full of hicks who proudly display Confederate flags." It didn't specify Minnesota or North Dakota.
Which was in reply to this "Why would you say this in Minnesota? People there don't give a crap about Confederate statues." in a thread about Trump giving a speech in Minnesota. Now granted other northern states are like that, just not the one that this thread is about.
Point is, this kind of rhetoric isn't likely to help Trump in Minnesota since even the rural Trump supporting areas in Minnesota are mostly neutral on the Confederate battle flag but could hurt him if it increases turn out in the twin cities against him.