Did you even read that?
"They cannot say whether the laws, or some other factors, are the reason for a lower rate of firearm deaths and that there are exceptions."
"Because such studies also consider suicides in calculating firearm deaths, critics say it is misleading to cite them when arguing for ways to prevent mass shootings. Suicides account for the majority of America's roughly 30,000 annual gun deaths."
"Authors conceded their scoring system "has not been validated." "
You can point to some study, I can point to the high number of gun related deaths in cities such as Chicago, LA, and New York as how strict gun laws do not reduce shootings by a significant amount.
They probably do reduce the number of suicides by firearm, however.