The M1 is an Arm+ in the sense that it supports a stronger memory model option that plain Arm doesn’t, and it’s this feature that is used by Apple’s OS and the Rosetta translation engine that gives the performance boost for x86 translated programs.

Of course the Rosetta isn’t needed by Linux and assuming that all software is recompiled for Arm natively then you probably wouldn’t need it, but I suspect that is what the GP was referring to.