This code has to run inside their Worker's platform; _technically_ you can compile Go to WASM and get it to run; but practically it is Javascript only.
IIUC this particular product runs in Linux containers, not in V8 isolates like Workers uses. The upside of this is broader ecosystem compatibility (you can use whatever language you want even if it doesn't compile efficiently to Wasm); the downside is that each container instance runs in a particular data center and you have to worry about the latency implications of that, whereas every Worker runs in every location.