It does look very thin compared to the one which held the record last. Maybe rather than inherently reaching that size, there was some sort of genetic issue. If the dog didn't feel like eating much, or wasn't fed enough, I would expect that would hinder growth normally... and if it was caused by some undiagnosed condition later in life, the amount of weight lost would seem too drastic not to notice.
Though on the other hand... some people are just always really thin. I guess the same could happen in dogs.