Normal configuration of a PHP server is to not run any PHP code and serve a static html file?
This is a seperate chained exploit itself, seemingly executed by a nation stae. There are thousands of exploits infiltrating web servers around the world daily, and they arent php2shell.
You only care about this because it falls into a weird viral narrative about "AI saftey".
Chained just means they used php2shell to run a local privilege escalation.
If you want more than that you need to chain an LPE. Which are plenty these days sadly.