I think this excuse was a ruse/part truth on the part of Gabby, as she likely did not want her father to know about the Moab DV stop. My own best guess is that BL’s parents flew him home, hoping for a break up between GP and BL, and they did in fact move some of her belongings. She was not comfortable driving the van, though, and probably wanted him to come back. So he does. Would that it were otherwise, but he does return, they check out, and the rest is tragedy. Compounded by the fact that the Moab DV stop may have afforded BL a self-defense claim for GP’s death. I suspect that is what he told his parents, anyway. It would explain lawyering up so quickly, not responding to GP’s parents, the odd early statement about how this was a difficult time for both families, etc. If they also thought he might be beginning to think about suicide, I could see them move into protect BL mode. Maybe they sadly believed him and thought that she’ll ultimately be found, but they don’t want to hurry the process because they knew he’d be the prime suspect. Idk. Moo.
I can go along with most of that, but I can't imagine anyone, not even the most protective helicopter parent, could stay silent if they thought she might be missing and he could help locate her. The only sympathy I can dredge up for the Laundries, and it ain't much, is if after they got the text from GP's mom BL told his parents that he killed her, and knowing nothing they could do now could prevent that, they went into protective mode for their son. Still reprehensible, but not as bad if they thought she might be lost and in danger but did nothing.