The remaster of PaRappa the Rapper which launched a year ago didn’t improve on the original other than adding making the graphics nicer, and hackers have found out why. The game you have been playing is emulation of the PSP game with an extra package of HD graphics.
It appears Sony created a PSP emulator on which the game runs, but as the engine is now freely available hackers have been using it to run other games on PS4 including Patapon and Namco Museum. ArsTechnica say the hackers are looking at the Asia-exclusive physical edition of Loco Roco 2 Remastered to see if that’s running a newer version of the PSP emulator.
We gave the remaster 8/10 in our review saying it “plays exactly like the original”.