I don't know where this myth originated from but I have seen this in multiple places. Even if you think about it 2d numpy arrays can't have different type for different columns.
It's in the documentation.
I just learned pandas recently, and I would have said this same thing. Not because I read through the numpy code, but because I read the documentation.
Is it wrong? Can't a user pick up a new tool and trust some documentation without reading through 100's of libraries built on libraries.
When was last time someone traced out every dependency, so they can confidently say something is "Myth".