I think she's more getting at the idea that even when I write as a woman I am writing as a man writing as a woman, so it's informed by my male conceptions of how a woman might view or interact with the world.

Same applies to anything really.  A 25 year old writing as a 45 year old is trying to guess how someone 20 years older might feel.  A 45 writing as a 25 year old is trying to recall how he/she saw the world 20 years ago.  A middle class American writing as a poverty stricken South American in a war zone is trying to explore how he/she would feel in those very different circumstances.  All of these things, their understandings of these things, would be shaped by their own experiences in very different times and/or circumstances.

I don't think it's exactly weird when a man writes exclusively as a woman or vice versa but it is unusual.  Logically the easiest most natural way for a person to write is basically a self insert.  The easiest viewpoints to explore are your own.

But they're also the most boring to explore because you already know those roads.