The article explains why that's important in the way the author defined the difference between framework and library. In a nutshell, as defined by the author,

The article explains why that's important in the way the author defined the difference between framework and library. In a nutshell, as defined by the author, a library is a cog which is included by your application and can easily be replaced if it's not being maintained anymore, whereas a framework is the system within which you create your application and switching to a new framework would require essentially rewriting the system (and throwing away what you learnt about how you developed your current app and having to learn the way to develop with the new framework). Whether you agree with the author's definitions or not is irrelevant to the piece. What is relevant, however, is that one can be far less judicious when including a library, because you can simply replace it in the future, whereas you need to be far more careful when switching to a new framework because it's not as easy to replace.