It may be possible that they developed their internal compass due to their nomadic lifestyle and the use of absolute directions within language resulted from that (rather than vice versa). I have no idea if this is the case.
Seems unlikely to me: there are many nomadic tribes, but this linguistic particularity and these abilities in spatial orientation were only reported for this tribe (AFAIK).
suggests that speakers of all these languages share the good spatial orientation abilities. Anyway it's true then that my argument doesn't hold. One should first verify if there is a subset of nomadic peoples that lack this language feature, and that they have poorer orientation abilities.