Insults are abuse. Skittles are food. Flipping off a horse in a national park is a crime. Two drunk people screwing are mutually raping each other. You can do all kinds of magic with words and categories. Some would call this magic "equivocation."

Even if I thought that insults over Twitter counted as abuse (I don't), 'insult' is the obviously more accurate and descriptive term, and one would only use 'abuse' if the aim was to blur the line between insults and other kinds of abuse.