A muffin top doesn't make someone look fat. A muffin top is the outcome of someone BEING fat, or having excess fat from tight pants, around their hips that can show through your shirt in some extreme cases.
What's you definition of thin then? visible ribs, no breasts or buttocks, the look that your break if someone remotely touches you? Do everybody a favor and just be quiet. If you cannot give credit or politely critique if you feel something is off or could be better, but instead choose to just insult people for what ever self-conceived opinion that few people on this sight share, then you have no right to speak.