Will a star-shaped Vdd net reduce ground oscillations?
I don't see any flaw in that post's logic. High frequency return currents will be confined to the area below the star point (the post refers to it as a local plane). I can't say anything about EMI cancelling each other but the reduced antenna length will definitely reduce it's gain.

That said, the author of that post repeatedly ignores the dangers of high speed design with this topology. By definition, if all the high frequency elements are isolated to the MCU, your high speed signals leaving the MCU will have terrible slew rates and likely fail eye diagram requirements. He admits that only close to DC signals will leave the plane.

As someone commented, there is no free lunch. There should be a an overall warning that this is only suitable for low speed. Simply put, if any of your communication signals require impedance control, avoid this topology.