This is a highly contested subject in linguistics and very much not definitive like the article makes it out to be. There are many languages where mama does mean mother, but there are many languages where it does not. In some cases, you get the opposite. In proto-Old Japanese, for example, papa meant mother. In Georgian, mama means father and deda means mother. I don't know enough about the mama/papa topic to comment further, but a quick Google suggests that this paper is somewhat well regarded by at least some people:
https://www.sussex.ac.uk/webteam/gateway/file.php?name=where...