To the first question, one can find hidden in the article: "Willett faulted the experiment because many of the patients were on the special diets for relatively brief periods - many were being released from the mental institutions. But about a quarter of the patients remained on the diet for a year or longer".
If people stayed on this diet for a year or so max of their 65+ years of life, this data seems utterly non-relevant to support either thesis. It is fundamental to know if the people (and how many) continued with the new diet for a sizable portion of their life. In any case the results should at least not include people that have been on the diet for just a couple of months.
It is hard to believe that a diet of low fat for just a random year in somebody's life (~1.5% of life span) would make a big difference against the remaining 98% of life spent eating fat. The question whether a low fat diet is better than a high fat one is very intriguing, but this data, as presented in the article, seem inconclusive.
It's not inconceivable though: I've friends who have lactose intolerance who once they have stayed off lactose for a while can then consume it relatively normally so long as they maintain a relatively low dose.
It seems possible that the body could "clean" itself during a period of low fat dieting sufficient that it can handle a normal Western diet for the rest of a normal Western life-span? If a mechanism for fat storing that was detrimental was related to one's age when the fat was deposited that might also explain how a short period of dieting would be beneficial over a lifetime.
Most everything [I've read] in dietary science seems inconclusive.