The meaning of the boolean is: *did it terminate the process?*

Why `.terminate()` would set the `returncode` to `1`? As `ProcessOpen.returncode` tells if a process is running, setting a value in `ProcessOpen.terminate()` implies that the process no longer runs. However it will actually no longer be running when `os.waitpid()` will be called and collect the child process (until then it's a zombie).