
It could be part of it. The injury that caused him to smile all the time could also be a contributing factor, considering it had hit his frontal lobe, and I'm pretty sure changes in that part of the brain often alter a person's personality and affect other things.
Is he a victim? Very likely, yes. They had no way of knowing that before he died and the bug crawled out. Of course, being a victim doesn't excuse his actions, but as readers we're allowed to feel pity for how he ended up by some part on his own.

Yeah, frontal lobe damage has caused dramatic personality changes. I remember in psychology class learning about how a kind love person turned into a violent drunk.
They still are doing research on how and why.
https://www.sciencedirect.com/science/article/abs/pii/S0010945218301540
Wait...was that stomach bug the whole reason for his uncle's crazy mad behavior and trying to take power?
...that changes things. He is a victim.