Everyone in modern day (Europe? and) Asia are supposedly decendants of Genghis Khan.
That's hardly likely seeing as he didn't live that long ago, and considering the enormous populations of Asia. As for Europe it seems totally unlikely since people have been living in parts of Europe WAY before Genghis was born, in areas his hordes never reached. And if this is true, then they would be descendants of Mongolians, not the man himself...goodness such a task would be...exhausting for one man.

Anyway, Magyars are not directly descended from Mongolians, but are a separate (if somewhat similar) people, who came from what historians guess is somewhere Southern-Siberia-ish, from the East side of the Ural mountain range. Of course that is one theory among others; tracing the history of a primarily nomadic people, with no surviving written history of themselves before they arrived in Europe is a daunting task.