Unless it was in a previous post I missed then he didn't establish anything. All he did was make generalizations about a large group from a limited experiences.
He did, and he prefaced it with that statement. I don't want to put words in his mouth, but I believe what he was intending to communicate was that since he has seen some officers who have little to no proficiency with firearms, he's want to ensure that all officers who used that weapon was proficient in its use.
I think that's fair.