This is too long but I wrote it and might as well post it. Genre: "media criticism":
I think there is a difference between a journalist and a memoirist, but not because of any dictionary or other definitions that attempt to place all nonfiction writing in one genre or the other. It's not that clear-cut. I'm not even sure what this discussion is about ... is it the responsibility of Mary to source her claims about Trump's alleged SAT cheating and apply contemporary "journalistic" standards to the claim? And that boils down to emphasis. If I were reporting it, I might protect the source, as that is a fairly common practice, yet the trend when I was a working journalist was that anonymity needed serious justification and was not a valid way to simply insert a "zinger" into copy that otherwise wouldn't see print.
To really vet the claim, you'd have to try to contact an awful lot of "Joe Schapiros" and document the effort. For one thing, you need a certain diligence to make sure that "Joe Schapiros" as a group are not being unfairly presented as potential cheats. There would be a methodology: Find all such "Joe Schapiros" within Trump's realistic orbit, check with each and probably apply some formula to evaluate their credibility. In addition, "reach out" (hate that construct) to Trump himself and ask if it's true.
I have seen "journalists" try to get away with the technique of quoting someone anonymously just because they like the idea of getting a claim into the record somewhere. Sometimes they have a job at a newspaper or magazine; sometimes they don't. Actually CNN does this quite a bit ... there would be stories that played it 95 percent straight, but then would get a real humdinger of a quote - often from several anonymous sources - and use that as the basis for a headline or a lede. And I don't even blame CNN or the NYT for doing this. But they overused it. I saw so many "White House in chaos" articles or editorials that I began dismissing most of what they said. NOT because I didn't believe it, but because I was hyperaware of my own desire to believe it, and didn't want confirmation bias to give me unrealistic hope that Trump was losing support. However, that's an awfully picky, technical way to go about consuming news media, and is probably fairly rare, as not everyone has spent decades in a business where they saw news being constructed, hour by hour, day by day.
Usually nonfiction can be broadly labeled "news," "commentary" or "memoir," but there are dozens of other possibilities - "history," "literature," "propaganda," "polemic," "rhetoric," "crowd-sourcing," "fact-checking," "travelogue," "color," "play-by-play" and on and on. But really there is a ton of overlap and hybridization. It's possible to take a journalistic approach to a memoir, for example. I think most writers want to be read and believed, and whether Trump cheated on his SATs is really IMO kind of a marginal claim. If I were editing a memoir that contained the claim, there's a good chance I would have queried it and suggested either supporting it or eliding it, depending on how it affected the readability and credibility of a manuscript.