I’m sure it was not. With specially prepared USB hardware you can read out main memory without any protection, and thus get around DRM. So they surely wanted to counter that.
Source? Very skeptical that what you said can work without running anything on the system, which would be detectable on its own.
It was an older flaw in Thunderbolt ports that could do this. Thunderbolt had the ability to request raw memory blocks over the DMA bus, which worked at the hardware level, completely bypassing the operating system. I believe this has since changed though.
You are right about USB, thunderbolt 3+PCI Express on the other hand allows very low level memory access, and in older implementations there’s nothing the operating system can do. But then again even if they force a specific thunderbolt configuration to prevent DMA it will still leave the “normal” PCIe ports as a way to access the memory outside the purview of the OS.
Don’t forget the SD card reader, also PCIe
