It's not in the posted link, but the author gave an interview to hackaday and addressed this. https://hackaday.com/2023/10/31/black-4-0-is-the-new-ultrabl...

> “Black 4.0 absorbs an astonishing 99.95% of visible light which is about as close to full light absorption as you’ll ever get in a paint,” said Semple. He notes this outperforms Vantablack’s S-Vis spray on product which only achieves 99.8%, as did his previous Black 3.0 paint.

Also, you yourself can buy Black 3.0 and 4.0 whereas one person owns the worldwide artistic rights to Vantablack (who is also banned from buying Black X.0)