AC Current Calculation from wattage and Voltage
The voltage dropped because there is a voltage drop in the wiring between the source and wherever you measured the voltage. There are voltage drops in each piece of wire and device between the generator and your appliance, but only the part between your meter and the appliance is large enough to measure. A 10 volt drop is a little more than would be desirable, but probably not too unusual.

The power rating of the appliance should be the maximum that any customer would see. Since your voltage is a little less than the maximum, the power is a little less and the current is a little less. Some appliance would tend to maintain a more constant power with varying voltage but many do not.