Lived in the South all my life (NC, TN, all over VA). VA is still pretty southern outside NoVA (where I currently live). Get south of Fredericksburg or west of Manassas and it's a very different state than what you experience within 30 miles of DC.
Still, it's not "Southern" in the same way as NC, AL, GA, etc, nor was it ever. It's not bad, it's just different.
I don't know what "post Southern" means. Sounds like a made-up term to justify an article where the author gets paid by the word.
Chris