The implication that I got was more that the clan divide exists only for gameplay purposes to have visually distinct subraces, while in context there is actually no combination of physical traits that are more or less likely to manifest whether you're a Helion or Lost. The race selection even says that in Hrothgar culture the distinction between Helions and the Lost are almost entirely an invention of scholars outside Hrothgar society attempting to interpret their culture. Also, in Bozja almost every Hrothgar character we see is ostensibly Lost, but several of them use Helion models, and other NPCs with Lost models use Helion names, further de-emphasizing any distinction.
eta: I swore I read it in the race selection but I can't find it there now; in any event the lack of clan divides is discussed in EE3.