This doesn't make much sense. If your notes are just going to inform something that is low stakes that will not be reviewed by anyone for accuracy, then it's perfectly serviceable advice. For the vast numbers of note-reliant professionals who need to be able to cite accurately to sources, this advice is childish.

Do you need someone else's system? No, and I didn't even know that this "problem" existed before reading this. The advice ought to be amended to encourage readers to build their own note-taking systems that make sense for them in context. Another useful nugget of advice is to tailor the note-taking style for the task. A freestyle method is certainly appropriate to support an off-the-cuff speech to colleagues, but isn't appropriate for academic or legal research.

The notion that structure is somehow bad is also not salient when the body of research becomes very large. If you are working with research from 100 different books or drafting a legal argument that cites 50 different cases, statutes, and other sources, then it really helps to have some structure in your notes so that it is easy to browse and search through them. When a mistake due to sloppy notes is on your ass and will have bad results for everyone relying on you, then making it "like play" rather than "like work" will only have catastrophic results.