The two snippets are talking about two different things.
For example, an Integer IS-A Number, so an Integer can be used in place of a Number. This means that you can add() an Integer instance into a List<Number>.
This is very different than replacing the generic itself. The second statement doesn't say that an List<Integer> and List<Number> are interchangeable. It is merely saying that an Integer can be managed by a List<Number>, as an Integer IS-A Number.