That seems wrong? As far as I am aware WebAssembly is completely architecture-agnostic, and Firefox has implemented wasm VMs for both x86-84 and ARM.
And even if it wasn't architecture-agnostic, it's pretty easy to translate restricted and well-behaved machine code between architectures. Much easier than dealing with javascript itself.
This is a false statement
> It requires x86/64 because it runs on WebAssembly.
What is the technical requirement behind this?
There is none, one of the main objectives of WASM was to be a machine agnostic bytecode, similar to JVM bytecode for example. People have even built wasm VMs on FPGAs