It's odd they flag suicide. The statistics there seem to correlate very well with average population density. So, they might have just accidentally measured the fact that smart people tend to move into cities if they didn't already live there.

Outside of that, and outside of COVID, the third leading cause of death for many years was "Accidental Self-Inflicted Injury." Just below Cancer and Heart Disease. The presumed correlations between higher intelligence and avoiding becoming a part of these categories seems like another accidental measure here.