Some thoughts on interpretive protocols and the reader's 50%
Spoilers: There is no conspiracy and he did not get killed by someone else.
Part of what's going on here, of course, is that there is a strong tendency for certain genre YA novels to privilege aesthetics, drama, and emotional response over plausibility. This is especially true when the kind of plausibility in question isn't regarded as common or interesting - say, knowledge of what tank treads do to the surfaces of streets, or the logistical base required to maintain an effective air force of any kind (hello, Hunger Games). Often this is even true on the part of the audience-- many moviegoers of my acquaintance will tell people to "just go with" various implausible things, because "it's just a movie".
Now, "It's just a movie," is not a very compelling argument. It's clear, though, that some readers or viewers will accept implausibilities and others will balk at them, and my hypothesis is that reader knowledge, expectations, and interpretive protocols determine their reactions.
If the filter a reader is processing a work through is "Stupid action movie," then they are going to have many of their critical faculties tuned down, so only the most implausible and ridiculous set-pieces will prompt a "Oh, come on!"
In contrast, if a reader is processing a work as serious mimetic literature, they're going to be hyper-sensitive to any perceived deviation from the world and human behavior as we know it.
My suspicion is that both my knowledge (of violence and the military) and my reading protocols are askew from the intended audience of this book. The author wants the set-piece to prompt an aesthetic or emotional response-- the protagonist's brother has been tragically slain! REVENGE!-- and not a skeptical or intellectual one-- Wow, that's some BS. What are the odds of that happening?
I strongly suspect that one of the things that's silently dividing the SF field internally, as well as dividing SF from YA, is the degree to which different audiences' reading protocols skew towards privileging aesthetics and emotion vs. intellect and pattern-matching. (I don't feel like this maps precisely or even closely to the Fantasy/SF split at this point, though people keep on trying to make the conversation about that, which I feel does a damn good job of obscuring what's actually in play.)
There's a whole 'nother post to be made about plausibility and the rhetoric of realism in fiction, but I don't have the time or bandwidth for that right now.