You can do that from a spawn point, but you can also do it from -anywhere- (EveryFrameScript, fleetAssignment attached script, etc.)
So, you could write an EveryFrameScript that used the above code to spawn a fleet every frame (not advisable though!) or you could attach that code in a script that runs when a supply convoy DELIVERS_RESOURCES (where the StarSector examples display a message). It would then spawn a fleet when that supply convoy reaches that station.
You just need to put that code somewhere where it will be
executed by the game engine; spawnPoints are handy and easy for this as they have the inbuilt advance() method that is called by the game engine automatically, but there is no reason you can't put the code in other places, and have it executed under different conditions.