I will admit to chuckling away to myself reading these, both the seemingly straight faced, naive suggestions of normal people situations and the obsession with D&V, emphasis on the D! 😆 The added details of him having been seen driving away from the area 30 mins before the service just adds to the mystery and clearly he didn't go incognito! All v strange.
The likelihood of it being an emergency for the children or his inlaws at a time when both his wife and father are unwell seems slim. Therefore, I deduce it is likely to be connected to one of the latter and as Camilla was at the service I think it is most likely Kate related somehow. If it was any kind of state business, they could surely have made a vague reference.