It’s completely different, though, whether you have a spacecraft-mounted firearm pointing away from the ship, or something that can be fired ABOARD the ship.
Did you look at the link? It’s an actual firearm - a combination shotgun/flaregun/handgun/machete, which could (theoretically) be fired aboard a spaceship. And obviously they had ammunition for it aboard too.
Also, the same page mentions the Russians have semi-auto handguns in their current survival kits. I know it’s Wikipedia, but even so, it doesn’t seem particularly unlikely to me.