Its a misconception that fluid means liquid. A fluid is a substance that has no fixed geometry, and conforms to the environment around it. If you adjust for time, you could make an argument that ice is a fluid, as glaciers flow almost like a river. Steam is definitely a fluid, as are all liquids and gases.
The article does talk about NASAMS, which is exactly what you describe. Its worth noting that a lot of the range is consumed accelerating the missile from stationary, gaining altitude, and flying through dense air. So, their range is much shorter than the same weapon when it is air launched.