As an LEO I have to agree. First, all officers (at least in my state) are competent with their firearms. That said, many of my fellow officers are not “gun guys.” Most officers are not armorers or firearms instructors. While they do qualify with their duty handguns every year, for some it’s simply not their hobby. A couple guys on my department are car guys, and why not? Another important skill an LEO must possess in enhanced driving skills. There are many facets to law enforcement that officers can be interested in other than guns. A few departments I know of have AR-15s in all their squad cars. Some officers personally own AR-15s and know quite a bit about them, others work to learn the platform and become very competent, while some only take the time to learn the basic operation of the gun and get other officers to clean their rifles. There is a reason most departments issue Glocks, and that is because they are simple to operate and easy to maintain.
I have worked in other occupational areas such as retail and utility services before getting into law enforcement. There is definitely more interest in firearms among LEOs than grocery store clerks or gas & water pipe layers. Let us not forget that terms like “expert” and “knowledge” can be very relative. Compared to your average person an LEO is likely to know more about guns than most people. However, it is not uncommon for a civilian to know much more about guns than LEOs. I would guess that a good majority of the LEOs I know personally own firearms; a little under half have a more than average interest in firearms; and about 15-25% could be considered firearm enthusiasts (relative term).
In closing, I would advise using the same level of skepticism on gun info from a random LEO as I would from any stranger in a gun store. Some really know their stuff, while others are talking out of their asses.