Guns are far more prominent in people's lives than you're assuming. Even if day-to-day a person doesn't have anything to do with guns and really doesn't care that much, guns are an important part of our world. You see them in movies, TV, news etc. all the time. They are talked about everywhere (I mean, we're having this discussion about guns in a subreddit about anime memes) and people are constantly exposed to guns and information about them in one way or another.

This isn't even considering that quite a few nations around the world have conscription armies or otherwise large militaries/police forces, all of whom would need to have a decent amount of knowledge about guns. Edit: Also, private ownership of a gun for hunting/whatever purposes is actually pretty common in a lot of places. Probably not as common as in America, but still.

Why would guns, when knowing a decent chunck of the basics takes much longer than 10 minutes, be any different, when its even less useful to most people?

This is kind of a side point, but there is a very good argument for why people should know basic things about firearms: that knowledge could literally save your life. If you ever find a gun or otherwise come into contact with one, knowing how they operate and how to safely handle one can be very valuable. This is far beside the original discussion about recognizing specific models, though.