There are two kinds of coolant long life and conventional.
Conventional coolant uses silicate salts as a "preservative" per se. They help to reduce corrosion and what not.
Long life coolant uses organic acid to do the same thing. The organic acid lasts longer than the silicate salts.
Mixing the two kinds of coolant is not recommended. Adding long life to a conventional car is not that bad. Adding conventional to a long life degrades the long term performance of the long life.
Conventional coolant is always green. Long life coolant can be almost any color (green, orange, yellow are the most common, there is also blue).
The label is warning against mixing coolant. The car probably had orange in it from the factory. Then someone changed it to green. The real question is whether that's conventional or long life green and unless you have the empty bottles from when it was filled there is no good way to tell.