I was pretty sure of myself when I first encountered this. However after reading usages for the word incidence, I realized it wasn't as incorrect as I had originally thought.
I've always thought of the word incidence as the term used to describe the angle of a airplane wing in relationship to the centerline of the fuselage. For example, "The wing incidence of a Piper J-3 is +2.5 degrees".
However, after some web searches, I realized my understanding of that word was incomplete.
Some usage examples from this site...
http://sentence.yourdictionary.com/incidence"We need your help to reduce the incidence of domestic violence in the boro."
"There was no increased incidence of liver tumors in rats."
This is in reference to an "occurrence" of something, which isn't that far off from the second of my original examples, which is why I started wondering if it was really that cut and dry...
I guess what I'm saying is, that while my suggestion of 'incidents' would definitely be correct, I could see where using 'incidence' in that context, perhaps with a slightly different sentence structure, wouldn't be completely wrong...