Understanding full well that these are pretty artificial results, I'm surprised at just how well Node and Python faired against Go and Java. For all the default assumptions around languages that folks have, they've certainly held their own here.
As others have mentioned, the results come from the difference between async concurrency vs "lightweight threads" (in Go and Java).
In the nodejs test, there's very little javascript code being actually executed here. Whats really being tested is nodejs's event queue (libuv), which is written in C. And its being compared to Go's coroutine system - which is also in C. But, if I recall correctly, Go's threading model includes a preemptive scheduler (which is very complex) and it allocates a stack per goroutine.
This doesn't test if Javascript or Go code is faster / more efficient. There's almost no javascript or go code being executed here at all. This is testing the execution engines of both languages. Go's execution engine has more features, and as we can see those features have a cost at runtime.
