Not counterfeits. Most probably the measurement didn't follow the specifications from the each battery's datasheet.
Each manufacturer specifies the exact conditions for how to charge and how to discharge their battery in order to get the Ah, by each model of battery. If not done as in the datasheet specifications, there will be different results.
Otherwise, it will be like measuring the volume of air from a car tire, and saying the envelope is fake. It depends of the pressure it was inflated, and the temperature.
Similar, the Ah written on a battery is not an exact value. The Ah is a number specific to the charge-discharge process, the currents used, and to the internal temperature of the battery.