He is not wearing a keffiyeh in that picture. A keffiyeh is a square scarf that is worn on the head.
In that picture he is wearing a non-square (fringed) scarf, and around his neck.
Only a nut would look at that scarf and make the leap "Yasser Arafat" -> "Palestinian Liberation Organization" -> "terrorist" as you do.
TV cook Rachel Ray made an ad for Dunkin Donuts a few years ago, in which she wore a scarf around her neck. The Trump-supporting type nutcases came out of the woodwork and said she was wearing the scarf to support the terrorists. You can see a sample of it if you Google "Dunkin Donuts" "Rachel Ray" and "keffiyeh". Most of the articles are by people who appear on Fox News regularly.
Only a wack job makes the leap from a math professor who is presumably an American of Italian descent that wears a scarf to the scarf being a keffiyeh! That Yasser Arafat wore! Who was in the PLO! Which is proscribed as terrorist! By make the leap I mean make the leap like you did.