In my eyes there are two things that are a big deal in a child calling another man dad. That is when the children are young enough to be confused by that and to believe that the person in question is their actual father, and then when they have an active father in their lives, and then its disrespectful of the actual parent child relationship.
I do not really have a problem with a child calling a stepfather "dad" when their own parent is absent from their life and its clear that there is no confusion about who is or isn't the child's biological father. This guy has been in jail for nine years and could be in for another year or so yet. I don't have a problem with this child calling her stepfather, dad.