Yeah, you can't pop on a PS2 disk into a PS5 and have the game running as if it were a PS2, that's not what's happening. They are instead giving two downloadable PS2 games to PS Plus Premium subscribers that can run on the PS5 via the "magic" we call emulation. Something similar has already happened in the PS4, where they sold PS2 games digitally. What is being discussed here is that the emulator (the program that allows PS2 games to run on other hardware) that is being used on the PS5 isn't good and doesn't have much effort put into.

Side note: there are two important factors on whether or not it would be possible to put PS2 discs on a PS5 and play them directly. The first one is whether or not the PS5's disk drive supports DVDs (PS2's disc format). Fortunalely, this checks out. The other factor is Sony's willingness to make the PS5 recognize PS2 discs and play them via emulation. It's not like Sony would make any money with such efforts, so don't expect them to do this anytime soon.