IIUC the idea is that when the dark matter particles decay, they produce a pair of bottom and anti-bottom quarks, and when these new particles colide they produce a pair of gamma rays. (Also, there is similar processes with W- and W+.)
It's super weird that he paper has only one author. Now most papers have like 5 authors. Is he analyzing the data from another team? For an experimental paper I expect even more authors.