I wonder if this is slightly mangled over the years?

MS-DOS wasn’t a specific IBM PC OS, it was designed to be generic 8086 OS. It was up to the OEM to adapt the machine specific code (mostly in IO.SYS / IBMBIO.COM) to their system. IBM owned IBMBIO.COM, and some of the utilities like MODE and FDISK, and early on Microsoft didn’t have its own implementations to offer for people building generic PC clones. You had to write your own, and hope they were compatible. Microsoft did eventually offer a generic MS DOS with an IBM PC type IO.SYS and reimplementation of the utilities, so perhaps those are descended from Compaq’s versions?