According to the story linked on the front page, Ryan and Chad Hall's dad is a 3:07 marathoner.
The fact that Ryan and Chad are both highly successful distance runners (although of course to different degrees) would suggest there's something genetic going on there. It's no proof, since they have plenty of other things in common (since they were raised in the same household). But I doubt many people would guess that there's no genetic gift playing into it.
But their father trained as a runner and ran 3:07. That's a respectable time which requires both dedicated training and some talent to achieve, but it gives no inkling of the prodigious gift in his two sons.
I know nothing about their mother, and also don't know how serious the elder Hall was about his training, but do other people find the quoted fact surprising?