I have answered your support ticket with this question and I am adding my response here for anyone else with a similar question
Where the data comes from is not really relevant, what is important is that it contains the needed fields (columns).
Can you confirm that you have also copied the CSS from the demo? Also, the first combo uses load on demand, yet its template and the databinding expressions are in the markup. The Text and Value are set so the combo can continue working like a combo regardless of the elaborate display change. The Value, for example, is needed for the POST and so you can identify selected item, the Text is also there so the combo API can work.
I am attaching here a modified version of the demo that contains the styles, the script and data binds to a data set in the server code. I hope this helps you move onward.
Telerik by Progress