The documentation says multi-select is possible, even gives examples here: http://www.telerik.com/help/winforms/dropdown-and-listcontrol-dropdownlist-selection.html
I am using version 2015.3.1104.40 version of Telerik.WinControls for WinForms (I recently upgraded to the latest version).
I don't see this property anywhere under drop down list, nor does it come up in intellisense.