It might be a much higher frequency which you're not sensitive to. My Galaxy S5 had 240 Hz. You can figure it out using a digital camera. Set the shutter speed to e.g. 1/10s, and take a picure of a bright spot displayed on a dark background while moving the camere so you get "motion blur", and count the number of times the object repeats. Multiply by 10 and you have your refresh rate.