Here is my unqualified guess. Please take it with a cart of Himalayan salt:
The 4 wire Romex is the power feed, with the red being the switched live and the black the permanent live. The two wire is a feed to another outlet or device, and they might be using the ground as the neutral. That does not seem kosher but it's the only explanation I can think of.
Edit: You could disconnect the 2 wire romex and see what happens.
Last edited by impreza276; 01-10-2020 at 11:20 AM.