A way of reformulating the author's argument is to recognise that there exists an intermediate block of programs that do not appear in any source-code, and that's the re-scheduler in the CPU, and that you can't reason deterministically about its behaviour, because its state is common to all the processes hosted on the system at that moment in time.

Formulated thusly, the author's argument seems eminently valid to me, and exposes the old bug-bear: the root of all this evil is nondeterministic execution. Elsewhere in this thread I bemoan the defunct IA-64 (Itanium) architecture because it delegated explicating inherent parallelism to the compiler and allowed the core to be shorn of rescheduling circuits, and (it now emerges) enhances security.