A car is a vehicle. Even if it's used as a weapon, it's still a vehicle.
A gun is a weapon. Even if it's used to punch holes in paper, it's still a weapon.
The terms are not mutually exclusive.
You're not saying that a rifle isn't a gun. You're saying that a rifle isn't a weapon unless it's used as such.
Look at the vehicle analogy for a minute. Different vehicles are built for different purposes. Vans for carrying small loads, passenger cars for carrying small numbers of people, semis for carrying large loads of freight, buses for carrying large loads of people. Can you carry 100 people in a tractor trailer load in a pinch? Sure. Does it make it a bus? No. You could call it a truck. You can call a semi, bus or pickup a truck, but you can't call a car a truck.
Similarly, there are purpose built firearms. There are hunting rifles, military rifles, defensive handguns, target handguns, for example. There are some firearms that are simply not made for use as a weapon, like an olympic 22 target pistol- it is purpose built to shoot holes in paper.
So, sure, shooting a Glock 23 at a paper target doesn't mean it isn't a weapon. It's like using a semi to carry a pallet of lime when a pickup truck could have been used to carry the same load. A Glock 23 is a weapon. You can call it a sidearm, pistol, autoloader- it is all these things, but you ca't say it isn't any of those things.
But the 22 pistol or rifle that is purpose built for target is hardly suitable for use as a weapon. It's like breaking down the pallet of lime and carrying it on a formula one car. Yeah, it will work. But it's really not anywhere near its intended use. So, like a race car is not a truck, a target pistol is not a weapon.