The pre-made stocks that you buy at the store contain Mono-Sodium-Glutamat (Natrium Glutamat) in order to make it taste good. But, it appears the article is talking about homemade chicken stock where you put chicken and bones into a pot of water and boil it, so you make your own stock.
MSG should be avoided. It kills brain cells. Mono-Sodium-Glutamat (Natrium Glutamat) can be hidden under many different names such as hydrolyzed vegetable protein, autolyzed yeast extract, spices, natural flavors, etc.