It is the way the system is designed, yes.  The nVidia GPU is a co-processor -- it is not a true discrete GPU. All video output in this system runs through the Intel GPU -- there is no physical connection between the nVidia GPU and the displays, internal or external.  
Hey guys, I have a Dell Vostro 3500 with MX330 running Windows 10. BIOS\drivers were updated to the latest versions. Both, iGPU Intel Iris Xe and dGPU nvidia mx330 recognized by Windows and appear in Windows device manager as display adapters. However, it looks like only Intel GPU can display output on the laptop's screen, MX330 cannot. So my question is: is it architecture limitation of vostro 3500?
Vostro 3500 with mx330 display output