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This does not "disable" Intel ME. The ME is instrumental to the boot process and it is impossible to boot a modern Intel x86 system without it. It's quite tiring seeing x86 vendors continuing to misrepresent this.

See comment by bri3d below for details. It appears they're just sending a command to the ME politely asking it to stop doing things, maybe. Of course, this happens long after the ME has already done a great deal of work bringing up the system.

Of the three options for ME scope reduction, none are good and none actually "disable" the ME, but it seems like they've chosen the least effective/audited option of the three. I should add that if you don't trust the ME not to be owned, there's not really any reason to trust that it will honour a polite request to stop doing anything sent to it, and you can't trust it not to have compromised the boot process anyway, making this rather pointless.