Why did royalty from Saudi Arabia give them a wedding gift? It was not a state occasion, nobody from the Saudi Arabian royal family was invited to the wedding.

I suppose you could say technically she did not lie when she said the earrings were borrowed. All gifts received which exceed a certain monetary amount belong to The Crown, not the recipient, although the recipient has exclusive use of the gift during his/her lifetime. (Married-ins lose access to the gift if they divorce).