I don't know how to respond to the first half of your post because I am not 100% what your point is.

You seem to want to draw a line between political speech and non-political speech. Or perhaps you only want to include speech about policy as being protected?. I will give you the opinion of Robert Bork (a very conservative judge) on where that line should be drawn: "The category of protected speech should consist of speech concerned with governmental behavior, policy or personnel...Explicitly political speech is speech about how we are governed, and the category thereby includes a wide range of evaluation, criticism, electioneering, and propaganda."

The tweet was about race relations which is undoubtedly a political topic. It may not have been nuanced based on the 140 character limit and may be incorrect. But there are no doubts that it directly addresses a political issue and is policy related.