TCA9538: Power consumption of the device

See [FAQ] How do I Calculate Power Consumption or Current Consumption for my CMOS Logic Device?

(For such a slow I/O expander, only the resistive load matters.)

The value in section 6.5 is an electrical characteristic. It describes how much current the TCA9538 uses for itself.

The value in section 6.3 is a recommended operating condition. It describes how much load current you are allowed to sink into the output pins.