Advertising during deflated moods is explicity mentioned in the document according to Ars Technica, although the Australians' article is indeed behind a paywall.
"Facebook's secretive advertising practices became a little more public on Monday thanks to a leak out of the company's Australian office. This 23-page document discovered by The Australian (paywall), details in particular how Facebook executives promote advertising campaigns that exploit Facebook users' emotional states—and how these are aimed at users as young as 14 years old.
According to the report, the selling point of this 2017 document is that Facebook's algorithms can determine, and allow advertisers to pinpoint, "moments when young people need a confidence boost." If that phrase isn't clear enough, Facebook's document offers a litany of teen emotional states that the company claims it can estimate based on how teens use the service, including "worthless," "insecure," "defeated," "anxious," "silly," "useless," "stupid," "overwhelmed," "stressed," and "a failure."
The Australian says that the documents also reveal a particular interest in helping advertisers target moments in which young users are interested in "looking good and body confidence” or “working out and losing weight." Another section describes how image-recognition tools are used on both Facebook and Instagram (a wholly owned Facebook subsidiary) to reveal to advertisers "how people visually represent moments such as meal times." And it goes into great detail about how younger Facebook users express themselves: according to Facebook Australia, earlier in the week, teens post more about "anticipatory emotions" and "building confidence," while weekend teen posts contain more "reflective emotions" and "achievement broadcasting."
This document makes clear to advertisers that this data is specific to Australia and New Zealand—and that its eyes are on 6.4 million students and "young [people] in the workforce" in those regions.
I think it's naive to imagine that any of this data collection is in service of social media users or their mental health.