Not only that:

It uses some custom language (SOM), built the AST/bytecode interpreters for that on top of other systems (GraalVM and RPython) which prohibits some optimizations and may use some intermediate format (Graal IR).

And then compares results using a limited set of benchmarks (Are We Fast Yet).

Interesting, but all in all it's not saying much (imho).

As so often: devil is in the details.