The arguments in this blogpost are fundamentally flawed. The fact that they opened a bug based on them but got shut down should have raised all red flags.
When compiling and running a C program, the only thing that matters is "what the C abstract machine does". Programs that exhibit UB in the abstract machine are allowed to do "anything".
Trying to scope that down using arguments of the form "but what the hardware does is X" are fundamentally flawed, because anything means anything, and what the hardware does doesn't change that, and therefore it doesn't matter.
This blogpost "What The Hardware Does is not What Your Program Does" explains this in more detail and with more examples.