If you consider "pull trigger, bullet comes out" as "a pretty good idea how to use a gun" then yes, but I'm pretty sure anyone over the age of four could do the exact same thing having never even heard of Call of Duty.
Don't need to know a whole lot more to kill people. Of course, I have been watching violent movies my whole life. I couldn't tell you if someone with no access to violent media would know how to hold, load, cock, and fire a firearm. Or more importantly, feel completely desensitized to holding a firearm in the first place.
I'll tell you I felt super nervous transporting my handgun from my house to the gun range for the longest time, I even felt uncomfortable holding it.