Hi,
When you click the repot menu, the menu item only call the SSRS report not the RDP class. So, SSRS report is calling the report used RDP class and get the data.
Menuitem -> SSRS report -> RDP Class (RDP class <-> Contract <-> UI Builder)
But, controller is different. It is only calling the SSRS report (it is simply doing the menu item report calling job).
Please refer the following links
daxture.blogspot.in/.../rdp-contract-ui-builder-and-controller.html
stoneridgesoftware.com/understanding-report-controller-classes-in-dynamics-ax-2012
Thanks,
Hari