It's a 4K-capable console. As far as I know, every AAA title released this year has had 2K, 3K or 4K support on the Pro, which makes Codemasters look like the lazy unprofessional studio I am beginning to suspect they are, given all the backward steps they took with this game and all the unfixed bugs and questionable design decisions in past titles.
The graphics "boost" you mention is improved AA and a more stable framerate. Very, VERY weak Pro implementation IMO and not worthy of the "Pro Enhanced" label on the box. On top of that, besides the nice lighting engine, the game looks terrible.
Codies mentioned that they "might look into" HDR in the future (although that also works on vanilla PS4).
It's hard to believe that a AAA game like this was released in June 2017 with next to zero pro support.
4K on PC and 1080p on PS4 Pro? Pathetic...