I’m sorry. I know it’s a Southern tradition to refer to your father as Daddy. It’s a entirely different thing for a person to refer to their daughters’ significant others’ father as the guys daddy. If Mama Spivey has known the family for years, then she would be referring to the man as Jim Bob.
Justin is obviously just a child in her mind. She definitely makes him sound like one with this tweet. If he is old enough to court her daughter, then he’s an adult male, and in their patriarchal world, she should be referring to him in a more respectful manner.
On the other hand, the Duggar’s treated Derick as a child too. I still remember that horrid Happy Happy song where Derick jumped in with the offspring and serenaded Ma and Pa Duggar.