An article about oceanic history I'm having to read makes the claim that the Vikings thought they'd reached Africa when they got to Newfoundland, since at the time there was not much of a concept of finding completely new lands accross the ocean, only of the ocean connecting already known places. The author doesn't elaborate however, and doesn't provide a citation, so I'm wondering how much truth is in this.
There's no record of Viking Age Greenlanders making the assumption that North America = Africa. It seems like your article is based on dubious assumptions, hence the lack of citations.
Vikings based out of Ireland had traveled down to West Africa, but they would have conceived of that (correctly) as being the opposite direction from Greenland and Vinland. The Greenlandic Vikings seem to have recognized that they were discovering something that they hadn't previously known as they sailed along the North American coast, which is why they attached such import to naming it.