It sounds like you are downloading a REPAINT for that aircraft and that the text in the REPAINT description is telling you where to buy the aircraft that the REPAINT you are downloading belongs to.
As mentioned by FlyingsCool5650 in his post, there is NO free Piper Warrior. You have to buy it.
If you are putting a REPAINT into your community folder or the onestore folder you will see no such aircraft in the sim - because that folder you are downloading only contains the texture folders and not a Piper Warrior 3D model.
Also - any REPAINT you download is going to be for a specific aircraft model - in your case it looks like the paint you are downloading is for the JustFlight Piper Warrior - so that paint will ONLY work for the JustFlight Piper Warrior.
I hope this is clear