I'm beginning to wonder if this statement might be extended to include their views on Elizabeth, as well. I find the Smart's adamant denial of any possibility of a boyfriend somewhat odd. Of all the possible scenarios, this seems to be the one that they have the most difficulty talking about or even considering.......the possibility that she might have had a boyfriend. I wonder if this reported total lack of interest in boys has been confirmed by others with whom she might have been more open.
I think this statement was just an awkwardly worded reference to what police have told us -- that one of the reasons MK was kept apart from her family was so that her memory of events wouldn't become tainted by conversations with family members. The "we haven't asked her any questions" line is probably the same thing -- investigators had asked the family not to question MK about the abduction, so that her recollections would be fresh and untainted when she was interviewed, and the family complied with that request.
I also recall an interview with the parents the first weekend after the abduction when they implied that they were trying to shield MK from the gravity of the situation -- presumably in large part for her own sake, but probably also so that she didn't turn into a hysterical basket case before investigators could conduct interviews and get all possible information from her. That could help account for why the word "innocence" popped into Mr. Smart's head when he was groping for words.
Remember that Mr. Smart has been through an incredible shock, has been getting very little sleep, is not experienced with giving interviews on national television, and may well be taking some sort of tranquilizers that have been prescribed to help him cope. I'd be alarmed if he WASN'T somewhat incoherent.