The fact that "Dutch English Canadian American" isn't used as a demonym by anyone anywhere is the reason I thought the joke was "obvious" (this isn't meant as a justification for the comment, just to elaborate in the hope of making it more clear).
Oh and last point - Dang is one person, not an army of people. The Trump thread is very very busy, so I presume he is busy. It's unreasonable to expect real-time or even "quick" addressing of every issue you perceive.
