Common descent means having a common ancestor. Humans and Neanderthals have a common ancestor.
This has been explained to you; what is the objection you have to this term?
A closer look at your illustration is helpful in understanding the point. Thanks. The word "related" is what causes confusion. One can be descended from another, or not be descended from another, and still be "related" in either case. But there is a sense in which one can say humans and Neanderthals are "not related," namely in the sense of direct descent.