Its done with the RadAjaxManager at the top...see how it links the radgrid and the details view (which lives in the window) together and visa versa? ...so also notice the grid has postback set on client row click. So you click a row, posts back, sets a session variable, and the details portion is databound to that session item.
What is it you need to do?...grid editing? There are much more elegant
(and faster) solutions for stuff like that.