The spread of Mississippian Culture

https://theconversation.com/cahokian-culture-spread-across-eastern-north-america-1-000-years-ago-in-an-early-example-of-diaspora-130106

I was enjoying reading this article, especially as they did something rarely done: they showed a picture of an arrowhead. I don't know about you, but I judge arrowhead style to be a good cultural indicator. If you find a Clovis point, you assume a Clovis culture. Similarly, if you find a notched triangle, like the above, you assume a common culture. In this case we can call it "Mississippian".

OK, so here are arrowheads from the "Sinagua" culture, from near Prescott AZ:

Note that the small one (and it is pretty tiny) is a notched triange - clearly from some version of a Mississippian Culture. 

Question: Guess where else these arrowheads are found?

Answer: "Pre-Classic Mayan Arrowheads", retrieved from Google image search:

When I realized the authors were un-aware of older cultures than the Mississipian one, with these same arrowhead styles, I stopped reading. 

Should I be shocked the authors do not even know basic facts of their own subject matter?