Multiprocessing and parallel programming is a different thing from async/await, which primarily has to do with with green threads and coroutines. You're right that the ideas go way back (hell, Knuth was writing about coroutines in TAoCP in the 70s!), but this does not qualify.

Unix was originally green threads, at least in kernel mode: it was a non-preemptable kernel running on a uniprocessor. This means that kernel code ran until hitting a voluntary context switch. User space was preemptible.

(User space being preemptible doesn't really make a semantic difference to the shell & and wait examples, unless some of the commands contain lengthy CPU-bound loops.)