My Linux remark applied solely to the backdoor that used a ACPI table to make Windows install malware on every boot, which I had linked. It did not claim that installing Linux protected you from anything else.
That ACPI table payload is conditional and obviously OS dependent. Overall not a huge threat.
SMM interrupt code comes from the very same BIOS image and is executed at arbitrary times regardless of operating system. SMM code can do pretty much anything it pleases, it runs at the highest privilege and priority level possible.
Discussion of SMM interrupt code is irrelevant to the observation that installing Linux protects you from a Windows specific backdoor. That was not a claim that Linux provided safety against every possible backdoor. You seem to be trying to debunk a claim that no one made.
I think it's UEFI mounting the Windows partition and dropping some files there before booting the OS. ACPI executes on a virtual machine inside the kernel and afaik it's not supposed to be able to write to files.
