In the first Unix, starting a process from the shell did exec, not fork. When the "child" process exited, the kernel would restart the shell. All the process control stuff came when Unix was rewritten in C from the original assembly.
I know they have no code in common. I'm talking about the fact that both were multitasking from the beginning. You're talking about specific early shell behavior. Nothing to do with capabilities of kernel which provided multitasking for two terminals at once.
Processes (independently executing entities) existed very early in PDP-7 Unix. There were in fact precisely two of them, one for each of the two terminals attached to the machine.
