Apparently the results have a spread, depending on the CPU used to perform the benchmark - they appear to be testing from haswell to skylake so that covers a wide range of x86 hardware.

Matching ISPC perf in the low end, and being ~1.5x faster on the high end, while being able to target all hardware that Rust can target (arm, wasm, ppc, riscv...) sound better than ISPC to me, which works for x86 very well, but not so good for ARM, and not really at all for anything else.