Yeah, its a fun one, but it does have a logical reason.

PSX was the codename for the PS1, and what the internet community latched on to, especially after the PS2 came out and there needed to be clarity on which they were referring to.

One of the early PSX PC emulators decided to name themselves PCSX as an amalgamation of PC and PSX.

PCSX2's team wanted to make a PS2 emulator on par with/inspired by (and maybe forked off of?) the PS1 emulator and decided to continue the naming convention.

And now we have the dislexia-unfriendly PCSX2 name.