Briefly, the author's beliefs appear to be:
> If the elections are rigged how did he “win”
The election is partially manipulated by gerrymandering but won in the sense that Bukele's overwhelming popular support is real, and the gerrymandering only pushed him from "clear victory" to "almost total victory".
> If he is responsible for the crime reduction, how did he do it in such a short time
The crime reduction came because it happened at a time when both of its opponents (the gangs themselves, as well as anti-Bukele government forces) were weak. It may also have benefited from a decline in murders that had already started before Bulele took office.
> how were the police trained so fast
The police and army were less "trained so fast" than having been relatively competent for a while but hamstrung by insufficient political will/funds (this point is less well explained -- maybe because the gangs trade so much off honor rather than actually paying off economically, reasonable people find the police/army a more enticing career path?).
> If the original crime reduction was due to gangs hiding the bodies is it really that unreasonable to think that what actually is happening is that the government is more effective at hiding the bodies?
Maybe the government is fudging things, but even anti-Bukele organizations and media don't seem to think so, and Bukele's popular support in the absence of repression (yeah, Bukele is not a champion of free press, but he doesn't yet seem to police the actions of everyday civilians to the extent that they would all be scared and lie to a visiting ~journalist) suggests that the murder rate really is down, and not just faked.