The grandparent is referring to the fact the ARMv6-M and ARMv7-M architectures are Thumb only (and are different subsets of Thumb 1 and Thumb 2, to keep it spic

The grandparent is referring to the fact the ARMv6-M and ARMv7-M architectures are Thumb only (and are different subsets of Thumb 1 and Thumb 2, to keep it spicy); so a Cortex M has zero instruction set overlap with a pre-Thumb ARM core, even though both are "32 bit ARM."