I guess this article doesn't take into account the fact that CBS and Viacom have since merged. They're history looks a bit like an Alabama family tree with multiple splits and mergers.
This is very common in the entertainment industry. If you think the story of Viacom and CBS is crazy, look up the story of the Victor Talking Machine Company and its many descendants and “relatives”, including RCA, HMV, JVC, EMI, Capitol Records and many others.
This is how I felt weeding through all of it: https://thumbs.gfycat.com/MealyDishonestBadger-small.gif