One is hiding, and one is sneaking. It seems to make sense to me. Hiding is more cerebral, being largely a form of trickery (you pick the spot where the seeker doesn't think to look, even if you are the thing concealed); Stealth is more physical and active, training your body and instincts to avoid detection when doing something. Of course, as with many skills, it's not entirely true. There's a cerebral element to stealth, just as there's a physical element to Concealment. But I think the division works as is.
Edit: In fact, I think it makes an interesting choice of mode when trying to evade detection. Do you find a hiding spot for a while, then sneak out when it's cooled down? Or do you minimize detection by getting out as quickly as you can manage?