I contacted Dell and they said, the signal must come from the same source/port, didn't sound too convincing on the phone so I am thinking they weren't sure, but I may be wrong lah.
Their product page states:
Can you guys with this monitor confirm?
../azul123
Their product page states:
Picture-in-Picture and Picture-by-Picture Multi-Views: View a smaller subscreen within your main screen, or two screens at once, using intuitive onscreen controls.
Can you guys with this monitor confirm?
../azul123