I'm guessing this is based off of the spoiler for the Crystal Fair song in season three. I really like it. Twilight says something about Candace losing her magic and needing their help before the song. My best guess is that is has something to do with her cutie mark, a crystal heart.
IDK, the individual and species names seem to be inductive of their nature, personalty etc. So I'm convinced that the crystal ponies are literally crystal ponies. On the other I'm pretty sure that they wouldn't look like that. The blind bag toys don't even look like that. Then again the toy and show development teams don't seem to talk much.