I think that there's a real need to avoid plagiarism in answers, anywhere on SE. I also think that there is no need to reinvent the wheel. If the web has the answer, and there's little that can be added to that answer, then don't try. Providing the source of the information, preferably with a link, cancels plagiarism. Even the Help Center recognizes that answers will need external material. It does say to only use what's needed and to use your own words.
OTOH, the guidelines for good answers tells us not to provide links without context. The link could become unavailable, or even be deleted. So we need to include the relevant info from that source in the answer, so that the answer here can stand on it's own, if need be.
The older a technology is, in this case decades, the more likely it is that what the web has will be as terse as possible already. That leaves very little room for people here to summarize that info. (How do you summarize the overview of a summary?) For the question at issue, the reply could have been "An EXE renamed to a COM will not run in anything earlier than MS-DOS 2.11." Ok, I may have the wrong version of DOS, maybe it's 3.21, I don't remember. Nevertheless, that literally answers the original question.
To provide more info, and make the answer worthwhile, the deleted answer here provided more background, gathered from the web, and reduced it reasonably. In the form presented here, the answer includes proper source citation. Comparing the answer here to the cited material I'd say a credible job of condensation was done. Maybe there could have been more background, maybe less was needed to answer the question. Some "wiggle room" needs to be there to avoid simple answers that "work" for the OP but do nothing to make SE better. I suppose the answer could have added other material, not found in the citation, such as the "magic letters MZ are for the creator of the concept, Mark Zbikowski," but that's probably too much trivia for the answer anyway. It was a good, non-plagiarized, answer, and would have gotten my up-vote.
My opinion, flag it and get it back. It's better than what's there now.