Wattage of DC device is not equal to AC
This is a constant current driver that regulates its output voltage in order to generate the specified current.

30V is the maximum that your driver can output in order to drive 700mA through the LEDs. In practice, it will usually output a lower voltage depending on what sort of LEDs you have connected.

However, 5.6W would suggest an output voltage of just 8V, which is well short of what you'd expect to see across ten LEDs wired in series, so I suspect that either your device is not measuring what you think it is or your LEDs are not wired in series.

Use your multimeter to measure the output voltage across the LEDs and see what you get. Assuming you are still getting 700mA through the LEDs the actual power will be 0.7 times the actual voltage.