there's certainly a technical difference between assembly and machine code, but it's pretty common to use the word "assembly" by metonymy with the latter

> the OS is not doing any “direct execution”

OSes have native executable formats for which execution most certainly has less steps than executing a .js, a .jar or a .sh, which I would absolutely call "direct execution". The criterion can be defined I would guess as - does the OS / environment need to launch a separate process / specific steps such as setting up an interpreter before getting to the code you want to execute ? but most likely there's a finer distinction to be made.