I'd think tutorials would fall under theoretical because if it gets too practical, are you not effectively writing a how to guide?
I'm not really sure the four categories fit into that quadrant scheme as well as they'd like.
It's not theoretical knowledge in the sense of "theoretical/applied physics", but rather theoretical knowledge because there is an extra step between it and application.
So if I give you a list of functions in a module/class and just tell you what they do, that is more theoretical than a code block that you can cut and paste as running code.
I'm not sure how else you would label this axis, theory/practical seems just fine.
Practical knowledge is knowing how to do something - tie your shoelaces, instantiate a model class, authenticate to an LDAP server.
Theoretical knowledge is knowing what is the case - that the cross-flow valves must be closed at take-off, that everything in Python is an object, what a Python property decorator does.
Technical reference is theoretical knowledge (that you apply in practice), as is explanation. Tutorials and how-to guide contain practical knowledge.