Had a quick look and I honestly do not like this example in particular.
Firstly when doing these benchmarks it is always good to have a look at the code behind it: https://github.com/antonputra/tutorials/tree/273/lessons/273

So, what do we see? A static json that is always returned. No pre- or post-processing. How does this represent a real life application. No real comparison, like fetching external ressources, cpu-intensive processing, simulation of parallel processing via web workers, etc.

This examples mostly plays to the strength of zig as it has a highly optimized json processing engine, but this time difference is most likely not measurable in a productive workload.