IF there are people involved in a situation where there's a risk of death, that's an objective fact. There is no 'correct classification' issue here. The article collects all shootings that happen on school properties, you can derive subcategories from that. On the other hand, if your selection criteria is, say, 'shootings where someone tries to kill as many students/teachers as possible' you'll omit a lot of very real shooting incidents. It's better to have more data than less.