I have problems with Carroll's coach's statement. I assume when he says sea level he means born at sea level. Well, were the Garcias of Spain born at sea level? Caroll's not by far better than them. (Oh, wait, maybe they're not clean, I don't know). OK, Marius Bakken and Adam Goucher were born at sea level and I'd bet lots of money that they don't do drugs. Carroll's PR's aren't much better than theirs. Yes, both of those guys now do training at altitude, but don't virtually all world class distance runners do at least some training at altitude?
As far as clean, sea-level, world-class 5k guys go, Carroll may be part of a very small group, but he's not the only one.