Pixel art is when the artist manipulates each and all pixels of an image with limited size and palette. When you’re using a tool that introduces any unwanted colors (it can be anything from regular brushes, smudge tools to transparency effects, or even resizing with anti-alias), you’re defeating the whole purpose.
 
After you pointed out, I can see now that some of the lines are re-traced by you, but since the base is still just a re-sampled image, it does not fall into the pixel art category.
 
Here’s a really good beginner’s guide that explains all the basics, pitfalls and things to avoid: http://pixeljoint.com/forum/forum_posts.asp?TID=11299

@Background Pony #7B9A  
Yes it is you can clearly see the pixels I used.

@Ponies from the underground  
Its really not.

@Leon, the Prony  
Yes it is.

This is not pixel art.

@JP  
Actually that image came from the show itself.

I don’t think that taking someone’s vector (>>1490850 I guess, you aren’t crediting the original artists) and running it through pixelate filter turns it into actual pixel art, nor it makes you an artist.