What? No.
The Nyan Cat .gif was created by
prguitarman; you're talking about the song. Plus he links to the song's origin and has stated that he wanted to license it out for use in his iOS app but couldn't.
The deviantART user is apparently upset that prguitarman hasn't "mentioned" daniwellP or Hatsune Miku (which is a vocaloid, not a person), despite prguitarman linking to it.
Quote:
It's just a shame that the Nyan Cat is getting more credit(and money from t-shirts, merchandise, etc.) than daniwellP and Hatsune Miku, the original composers.
None of the merchandise uses the song. And they're not the original composers of the .gif (Miku isn't even a real person; someone just fed "nyan" into an application a bunch of times).