Reading glasses with negative corrective power?

First of all, I’m hoping this makes sense in English—I’m not sure whether terms and units of measurements are similar in the rest of the world…

As I understand it, reading glasses usually have positive corrective power (they are labelled e.g. ”+2.0” or ”+1.5” or something). I am nearsighted, needing glasses of -2.0.

Since I usually wear contact lenses, I didn’t really want to spend too much money on glasses, although a pair is nice to have. Whereas there are reading glasses with a certain corrective power available everywhere, they are usually custom-made when you are nearsighted—usually. I came across a cheapr pair that was -2.0, and bought it.

However, the label says they are reading glasses, and: “Warning: For near vision and reading use only.”

When I wear them, I can see just fine again. Why does the label says they are reading glasses, when they help me to see at a distance?