Yep that seems to be the same info as the commandline tool i posted.
So if you disconnect the screen, it isn't listed anymore in System Information? (Just to verify it is actually the LG 5k that is listed)
FWIW, on my Macbook, the LG display is reported as follows (I'm on Sierra 10.12.6)
(Note the 30-Bit color)
Radeon Pro 455:
Chipset Model: AMD Radeon Pro 455
Type: GPU
Bus: PCIe
PCIe Lane Width: x8
VRAM (Total): 2048 MB
Vendor: ATI (0x1002)
Device ID: 0x67ef
Revision ID: 0x00c7
ROM Revision: 113-C980AF-908
Automatic Graphics Switching: Supported
gMux Version: 4.0.29 [3.2.8]
EFI Driver Version: 01.00.908
Metal: Supported
Displays:
LG UltraFine:
Resolution: 2560 x 1440
Pixel Depth: 30-Bit Color (ARGB2101010)
Main Display: Yes
Mirror: Off
Online: Yes
Automatically Adjust Brightness: No
Connection Type: DisplayPort