Pardon me for appearing cynical but...
If that's not evidence of contrived conversation, I don't know what is.
TMH innocently asked "was there anything you can remember triggering it"
knowing full well that she herself had triggered an almighty Explosion only hours before Allison disappeared.
In fact she had hounded him, berated him, argued with him, unrelenting, like a lethal obsession when he arrived at his parents place where the children were at that time.
He would have flown home in full rage. Probably leaving the children with his parents whilst he "managed" the situation at home.
IMO This argument was the trigger.