Oh, come on! Calling someone a maroon goes back to Bugs Bunny cartoons from the 40s or 50s. He would say, "what a maroon" about Elmer Fudd or Daffy Duck, mangling the word "moron", which is an ancient word. See
here. Whatever the origin of the Spanish "cimarron", it has nothing to do with it when Americans call someone a maroon. It is just a Bugs Bunny reference.