I'm sorry you're more confused than you were when you started!
The post is intending to talk about the topic of memory allocation in a general sense. The way that malloc works on any given system is implementation dependent, it's not possible to say "malloc works in this way" because Debian can differ from Arch can differ from BSD, etc.
It's not my goal to tell you exactly how modern malloc/free implementations work. I could probably be more clear about this at the start of the post.
The post is intending to talk about the topic of memory allocation in a general sense. The way that malloc works on any given system is implementation dependent, it's not possible to say "malloc works in this way" because Debian can differ from Arch can differ from BSD, etc.
It's not my goal to tell you exactly how modern malloc/free implementations work. I could probably be more clear about this at the start of the post.