Yup, there were at least 3 cases in my former congregation (all going on at the same time when I left) where an elder or MS was assigned to study with a so-called "fatherless boy" (i.e. he had a father but he was either not a JW or was DFed). I know for sure that in one case they were often studying alone, just the two of them, and have no reason to suspect that this was in any way unusual. In fact, I think the boy's mother appreciated it and viewed it sort of like free babysitting that let her get some errands done. When you think about the difficulties of a single mother raising kids, I can't imagine this is unique.
In this particular case, I remember an interview with the lawyer in which he stated that this was essentially what was happening - lopez was viewed as a fatherless boy because his father was not a JW, and Campos was assigned by the elders to study with him.