This seems like a misunderstanding, WebAssembly has nothing to do with PHP’s internal performance mechanisms. WASM is a compilation target, this means you can take code which needs to be compiled (like PHP’s core binary), and compile it to be run in a browser.

PHP in WASM means developers can run actual, real, native PHP code in the user’s browser, without the user needing to have PHP installed locally, or nginx, etc…

You could do that, but the post here is in fact about running PHP on a server on top of a Wasm runtime.

“At the edge” basically means “close to the user”, with the details left as an exercise to whoever is selling you their “edge.” In this case, it’s a Wasm runtime company.