I wonder how much of that ANS anger was fueled by guilt rather than long-lasting hate or animosity? People react to being cornered in different ways. Virgie basically blamed HKS for killing Daniel and we all assume ANS had major guilt over it. So having mom blame them for the death had to add salt to the wounds. When I feel guilt I don't usually react in anger, but who knows how others react.
If the hate video was orchestrated by HKS, then I think the old Shakespeare line "The lady doth protest too much" comes into play also. In other words, to "protest too much" is to insist so strongly about something not being true that people begin to suspect maybe it is true (the responsibility for Daniel's death, that is).