Yes.
So the author says that no school that allows armed teachers has ever had a shooting. Tens of thousands of schools that don't allow armed teachers haver never had a shooting either. The fact is that school shootings, while tragic, are also rare. So the author is stating the obvious, most schools don't have shootings regardless of whether the teachers are packing or not. What would be interesting, and which the author of the paper did not provide, was evidence that a shooter was deterred by knowledge that the school staff could be armed or evidence that an armed school staff stopped an active shooter in the act. We don't have that.