I think this is ultimately a "no shit Sherlock" kind of announcement- we already know all Xbox One games will work on Series X and Its all but been confirmed that all PS4 software will run on PS5.
Yes, the question of "upgrades" and "patches" to take advantage of better hardware is in question (and will probably be different from game to game), plus the systems might have some kind of baked in "boost mode" as well that applies to most anything- my guess- companies like CD Projekt Red will be real cool- and hand out 4k upgrade + GFX patches for free- others may seek to charge for this upgrade- but again, at least the base Xbox One/PS4 versions game will run on new hardware, no question. But naturally, I'm hoping that free patches becomes the norm, and companies will quickly be shamed out of any notion of charging for this kind of thing.
I don't expect Sony's policy to really be any different from MS's here. That would be a REALLY bad look, and they would get savaged if they didn't follow suit. The press release is just going out for Xbox because this is a MS marketed game, CD Projekt Red is being paid to make MS look like champs, and there just happens to be more official Series X info out there right now until Sony finally calls their own press conference, and as such, no one can current say much of anything regarding PS5 development.