The section "Common Ancestry" acknowledges the prior history. Though it feels a bit odd. "MS-DOS is there said to be variously a copy or clone of an operating system named CP/M" seems to gloss over the details by sticking specifically to Caldera's Consolidated Statement of Facts, and not mentioning QDOS/86-DOS.
But the author really assert that "DOS" is a very specific term:
> To me, DOS meant MS-DOS and its licensed variants such as PC DOS. DR DOS was no more a brand of these than juices pressed from soy beans, almonds or cashews are brands of milk. This is not to say they have no merit—some of those juices are more enjoyable than is most American milk—but they’re not different brands of the same thing. To me, DR DOS could not even be a candidate for consideration as another brand if it would always, as seemed likely, need special accommodation in anyone’s DOS programming.
so the idea of a "DOS market" doesn't make sense.
Further, the author probably places you into this camp:
> The preceding question seems to have got conflicted in the early 1990s—and may be still in the apparently growing community of retro-computing enthusiasts, some of whom are vigorously revising history, at least as recorded by Wikipedia, to favour DR DOS. The conflict I mean is that celebration of DR DOS as a compatible alternative to MS-DOS for running MS-DOS programs often coincided with requests that MS-DOS programmers should keep in mind what different writing may be needed for DR DOS.
The author appears to have a specific interpretation in mind, yes, and it doesn't match my understanding from the wet-behind-the-ears me at the time.
However, to be more clear, Apple DOS almost certainly was not part of the "DOS market" that the lawsuit concerned. You would have to care far more than I to resolve the underlying issues. I just know the linked-to text doesn't seem to have the ring of truth.
So I didn't understand the author's comment about DR-DOS being the imitator, at least not without acknowledging the prior history.