This quote ignores the middle ground of users who have a valid use case, but don't yet understand metaclasses. Not great advice for people who are trying to learn metaclasses.
There's a "basic" [1] understanding of Python's object model, one which understands that most of Python is actually syntactic sugar for calling certain special methods. For example, the expression a[b] is "really" just calling a.__getitem__(b). Except that's not actually true; the "real" object model involves yet more dispatching to get things to work. Metaclasses allow you to muck with that "yet more dispatching" step.
So when do you need metaclasses? When you need to do that low-level mucking--the kind of mucking most won't know about until actually needed. If all you know about metaclasses is kind of what they are, then you very likely haven't learned enough about them to use them to actually need them. Conversely, if you've learned those details well enough to need to muck with them, then you've also learned enough to the point that you can answer the question as to whether or not you need metaclasses.
[1] I suspect most Python users don't even have this level of understanding, which is why I put it in scare quotes.
Maybe he was also suggesting that people should generally not be using them. In my experience, it is exceedingly rare to need them. In 29 years of writing Python code, I think I've used them once or twice.