I believe that this question is asking about a conversation that happens between Max and Grim in chapter 21. The conversation occurs near the end of the chapter after readers find out that Killer Kane must serve out the rest of his previous sentence plus an additional ten years. Grim tells Max that Killer Kane is a accident of nature and that Max is nothing like him. Grim then tells Max that the only things he got from his dad were his looks. Everything else, especially his heart, he got from his mother. While this conversation may be brief, it is hugely important for Max's mental and emotional health. Max knows that his own grandparents are wary of him because of the way that he looks. Additionally, Gwen's initial reaction to Max was one of fear based on his looks.
This chapter also sees Kevin's condition quickly becoming worse and worse. Max may have survived his father's kidnapping, but his life still appears to be spiraling out of his control. His grandfather's kind words are a very needed emotional boost to a kid who really struggles to see himself in any kind of positive light.