As Mr.Cifaldi correctly pointed out, Sony's decision to use PCSX ReARMed is an interesting one. It gives legitimacy to the software as a functional emulator that is up to the company's professional standards. The use of this emulator also confirms that Sony is using an ARM processor of some sort in the system, though this was expected.
We also get some insight into the graphics quality of the PlayStation Classic. Mr. Cifaldi points out that the games look and sound accurate, which means they probably look blocky and pixelated in comparison to any of the modern consoles. Games produced for the PS1 used a resolution of 640x480 or lower, so blocky and pixelated is to be expected.
The overall visual experience will likely be similar to what you would experience gaming with a PCSX ReARMed emulator on Android. We can’t rule out the possibility that Sony altered the emulator to improve graphics performance somewhat. PCSX ReARMed is open-source, and it can be freely altered by Sony (or anyone else) to suit their needs, and it’s possible Sony did that here. Due to the limited resolution and quality of the source images in the games, however, any improvement would be limited. The PlayStation Classic is set to be released on December 3.