The conclusion is (emphasis mine):

Although the results of the study have yet to be published, scientists are already reporting a decline in insect cognition in the contaminated area of Fukushima Prefecture. "We can see correlations," Armant says. "However, a causal link with radioactive contamination has not yet been established. But since the area is no longer inhabited, it is unlikely that the effect is due to factors such as pesticides."

So, when people leave the area, insect cognition decline, therefore human presence improves cognition in insects.