That looks like a very nice display at a very good price but something isn't exactly right.
You obviously have it working and you didn't mention anything about the contrast adjustment so I assume that you are using the standard 10K potentiometer between +5V (Vdd) and GND (Vss) to supply voltage to Pin 3 (Vo).
The seller advertises this as a "Wide Operating Range: (-30deg C to + 70 deg C - Industrial Spec)" device and most of those devices require a negative voltage on pin 3 (Vo). The data sheet also shows that the "Wide Temp Model" requires Vdd - Vo to be at least 5.4 V which would put Vo at -0.4 V with respect to GND.
So it looks like this may actually be a mis-labeled Standard temperature version.
Don