We are all trying to get used to this new Music app, but I think that little icon instead the triangle indicates that the Music is actually on your device and not in the cloud.
The little icon represents an iOS device and that means to me that the songs are actually on my iPad. If I use the option to show iTunes Purchases, when those albums or songs appear on my iPad, I don't see that little triangle with the iOS device icon in it.
THis is just my assumption but based on the experimentation that I did, I think that's what they mean.