In short, a zettelkasten is not a life operating system. LYT is. Though a zettelkasten can include notes on literally any subject a person has an interest in, these notes are intended to yield something tangible. LYT is not bound by output, and thus includes more. People, projects, calendars, ephemera, the stuff we manage in our day-to-day lives, all of it can have a place in LYT. So, while both methodologies deal with the same "stuff"—knowledge—and both engage notes as their primary units for knowledge exploration, each has a different expectation as to what should be done with it all.
Author posits ZK is for writing, Milo's type of stuff not aimed at output but at 'progressing' in multiple ways. I'd assumed that would be clear to all. Any (p)km is geared towards action, or at least towards increased ability to act. It's rarely the aimed for ability is just academic written output. My pkm has always contained a 'get stuff done' component as well as a 'conceptual stuff' component. My ZK so you will is a trio (Notions, Notes, Ideas) of folders of networked elements inside a more hierarchically oriented larger set of folders (GTD like) to keep moving forward on everything I'm involved in. I've at times wondered what Luhmann did to manage his academic work, in terms of notes. Is there another kartei somewhere? It's one thing to write a lot, another to get it published / organise academic life.