A lot of people assume that because an individual is an LEO, they know about guns.
Many believe that if they are a gunsmith/gunshop worker, they know about all guns.
It would follow to many of these individuals who think this way that a person who was a combination of both would therefore be unfailing in their firearms knowledge.
Often, they are completely wrong on most or all counts.
Many LEOs know little about firearms, including the ones they carry everyday. The sidearm is just another part of the uniform that they have to carry.
Gunshop dudes are often at a total loss for accurate firearms info, especially if it outside fo their customer interest base.
Just because this guy is working on a lot of ARs for local PDs does not mean he knows what he is doing, or that he has correct technological info.