That was also my understanding; that the man was evasive. Given the weirdness of the claim and his evasiveness, I think the mother has done all we can expect her to do with that angle of her investigation.
I get the sense that she has her doubts about it but doesn't want to ignore the possibility, either.
Something to ponder:
The Martin boy also of West Des Moines and abducted about a year later was also taken from his newspaper route. Brian Bleyl was abducted from his paper route in Phoenix, AZ in 1981. A man confessed to the murder of Brian Bleyl to 3 different people; stating that the boy had made a homophobic slur to him. The boy's bike was found right behind his apartment some 20 feet away and the boy was seen at this man's door. The man's name was Stephen Wilson.
Stephen Wilson died in December, 1993 of AIDS and was openly homosexual. He was 44 years old. In 1990 he was tried and acquitted for the murder of Brian Bleyl due to lack of evidence. The boy's body has never been found.
If an MO appears to be developing here, you can note that all the boys looked very similar. Another boy, Marc Allen, who looked very similar to the others was abducted from Des Moines in 1986. In 1989 another very similar looking boy was abducted at St. Joseph, MN by the name of Jacob Wetterling.
Of all the abductions of this very rare type, there were only about 90 throughout the United States from 1981 to 1991. Only about a dozen of them are similar in all respects to these.