Looks like they’re definitely from the included blu-ray, and not the 4K UHD, according to this italicized note in the review proper.
The included screenshots are sourced from the included 1080p Blu-ray disc, which has itself received a fairly drastic makeover compared to the 2011 20th Century Fox release.
So if I’m reading that right, EVERY screencap on that site for that review of Star Wars: A New Hope is taken from the '19 transfer that’s on the blu-ray, and not the UHD.
Hopefully they do that for the rest of the OT and PT, too!
They did as well for the individual PT and R1. They are releasing daily reviews.