Its more so you misunderstood both the math and the case.. With granger causality you can not look at absolute numbers between different entities, thats not how it works. You need to look at how homicide rates chantge in the immediate time after a change in gun laws. If you looked only at homicide rates across countries you'd be doing "bad-science" as it isnt showing temporal causality.
Not in the least, I would change quoite a few things about the current situation and dont agree at all with the status quo.