Those of you who guessed it was kid!Jareth traveling through time - you were right! One of Jareth's coolest (if most underrated) powers is that over time; undoubtedly this took some experimentation with as a child to control so finely as an adult.
Great hypotheses, everyone.
Now, anyone want to take a guess as to who his father and sister are? Here's a hint: They'll be back!
Jareth and Sarah belong to Henson, Lucas, Bowie and Connelly.
Jadis belongs to Lewis.