Drops to 54 FPS with R&C and Returnal drops to 46 FPS. R&C stays very close to the target of 60 FPS, but Returnal can have some annoying drops in combat that would be largely eliminated with VRR.
Yes, Sony 1st party generally sticks to the frame targets very well, but they hardly the only studio to do so. Resident Evil Village non-RT mode is a flawless 60FPS on both consoles for example, not even a drop to 59 FPS in sight.
They are not guessing the numbers they have given, they compared like for like and used a range from what they pixel counted, just as VGTech or NXGamer do. VGTech is not perfect either, in the Mass Effect Legendary Edition comparison they completely skipped Mass Effect 2+3, and especially on 3 the PS5 has some severe framedrops. And "average" FPS is a poor measurement of a games performance, RE8 for example had an average FPS of 57.35fps vs 58.73fps, so that seems almost the same right? Expect in stress areas that gap widens to over 15% at times, which has a notable impact on the feel of the game.