I don't think it is meaningful to enable JS but disable WebAssembly, as almost all of wasm can be translated to JS anyway, as the older Emscripten did with asm.js.
Yeah it's really mostly just a (heavily) stripped down binary JavaScript with basic arithmetic and operations to modify an ArrayBuffer. With Wasm-GC it's a bit more of a binary statically, strongly typed JavaScript. Either way, outside of static, strong typing, the binary representation and SIMD support, it's really not exposing anything fundamentally new.
WASM isn't the reason this works. This could easily be written in pure javascript. The only thing WASM gives you is significantly faster WebWorker-like background threads, but ones that are still limited to WebWorker-only APIs.