The point is in reference to flohofwoe's earlier comment which stated "it's still fairly straightforward to map C statements to CPU instructions.". By pointing out the existence of vectorized instructions, which are entirely absent from the C standard, pjmlp was making an argument by counter-example. That while you can map C statements to CPU instructions, most compilers typically don't apply such a 1-1 mapping.

The seeming non-sequitur referring to the ISO C standard was because flohofwoe responded to the rhetorical question as if it were a normal question, leading pjmlp to restate the rhetorical question in a stronger form.