Currently I’m creating this table inside a new node called “Data Types”, and having all these data type nodes link to this node. But I feel it not so Zettelkasten-ly, as the concept of summary is not used in Zettelkasten. What should I do?
I think you’re combining concepts here (in terms of the workflow, I mean, not just your content).
Zettelkasten is for recording the ideas you take away from things. In this way, your individual course notes are more like Zettelkasten notes.
But these notes are meant to be used – to create connections in our thinking and come up with new ideas. The beauty of Obsidian is that it can contain both types of notes, and I think the note you’re describing with the table is this second kind of note.
Neither is “right” or “wrong”; they’re just different, and serve different purposes.