"One-off stories" is plural. You might argue that it is then an oxymoron in the absence of context, but the person you are replying to is clearly contrasting one-off stories with a general pattern.
Smaller children are at risk for coyote attacks. A 12-year-old boy does seem a bit unusual, but he wasn't paying attention to his surroundings. It may depend somewhat on whether the animal was rabid, or how hungry/desperate the animal was for food.