the device does only use +5V and GND for signalling.
Then it's not RS485, but certainly the pinout shows that it is.
In that case RS485+ = A and RS485+ = B I would say (A and B are the standard RS485 designators). IIRC if A > B by 200mV or more then you have a logic 1, A < B is logic 0.
So I'm wondering if you tie B to 3v3 and use a 0-5v signal on A it might work.
Rob