There's a pretty big hole in that story the granny used since monster meat is known to kill humans.
Plus the massive escalation the monsters keep on doing. I mean, after the first few times wouldn't the local monsters realize to not startle humans under any circumstances?
I'm also not really buying the whole humans are the REAL evil sctick when they're doing the very thing they claim only humans are capable of doing.
Despite 99% of humans being extinct almost every bloody monster in the story seems to instinctively crave human flesh which makes their side of the story a wee bit suspect. They don't even recognize what the scent is but know they want to devour it once they get a good whiff of Somali.
The story from the witches makes it worse since it's clear that a bunch of idiots read about a bunch of sentinel islanders, decided to not leave them the hell alone like they clearly want to be, and then blamed everything on the humans when they were the dumbasses that went to a bunch of people that would clearly kill them in fear upon sight. A fear that may be more justified than the monsters realize since they salivate at the slightest hint of a human.
I'm sure that humans did some things stupid but the monsters have clearly edited their side of things for better justification.