"Is it NOT appropriate to respond to the Professor & challenge his false assertion?"

Absolutely it is appropriate to respond and challenge. Heck, I even support what the student said.


The students method of response, is the crux of the issue. the way he went about his business was wrong, even if his message was correct.
Student comes off gloating the victory and badgering the professor. Also, no student should ever post a flyer or something else to a professor's door.

(Note: I also don't think the professor was right to post scripture against Trump, but his post was similar to Mike Lee calling Trump Cpt Moroni levels of stupid. . . )