Huh? Science does not need to have a plausible causal mechanism to observe something. For a very long time we had no reason for what causes mass, and yet we knew about mass. How about what causes energy, we have no clue as to what causes that. Are you saying energy is not a thing because there is no plausible established causal mechanism? I'm very confused as to your statement here.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3828709/
"The final GEE negative binomial model revealed 6 significant predictors of firearm homicide rates: gun ownership proxy (IRR = 1.009; 95% CI = 1.004, 1.014), percentage Black, income inequality, violent crime rate, nonviolent crime rate, and incarceration rate (Table 2). This model indicates that for each 1 percentage point increase in the gun ownership proxy, the firearm homicide rate increased by 0.9%."
Are you saying this did not find that the % of Black people in the population was a predictor?
Haha, I have no doubt that you are very confused. I personally am baffled as to your confusion though as this is something they teach you on the very first day of any stats or research course. Basic to any attempt to establish a causal relationship is a plausible causal mechanism. This is established with the guns/gun violence relationship. It is not established with the being of African ancestry/gun violence relationship, which is what he was clearly referring to.
You may want to refer back to woolfe's criticisms from threads past where you tend to get very confused and wrapped up in arguments that come from your inability to understand things that everyone else considers to be implicitly obvious.