Oh, I see what you see now that I actually click the link. $15 for the MYJG version. It’s sold by Cloudray and still shipping from China, they are just charging $5 for shipping embedded in the amazon price. I just checked, and the slow shipping that is $15 on Amazon is free shipping from Cloudray, so my rationale for not buying it was bad. Ordered direct and I’m now $10 poorer. 
It’s obviously not ethernet; there’s no PHY on the board, so they are using CAT5. The RJ45 is directly wired to the same wires going to the unlabeled chip in the picture above. I didn’t trace the circuit to know what protocols are likely running across those wires. I’d guess SPI or I²C because traces are shared with the in-box display, which would basically rule out current-loop or differential serial. I doubt that it’s remoting sense resistors but I could be wrong.
Looking at the board in the box, there’s one unlabeled LCD driver chip, and I think the contrast pot on the left is in the middle of backlight power supply drive; there’s a heavy trace from pin 1 on the LCD driver chip down to the largest capacitor on the board which makes me guess it’s VCC, and a via next to the pin opposite that I’m guessing goes to GND on the other side of the board (I didn’t unscrew the LCD board when I did the partial tear-down). All that tells me its probably a serial connection, not remoting sense voltages.
But I don’t care enough to put a scope or logic analyzer on it. 
Here is cloudray’s instruction for how to use the remote potentiometer:
