DATA is input/output, similar to GPIOs on ATmega328, for example. The datasheet for ATmega328 says DC current per I/O pin is 40mA.
Does that mean that the GPIO pin takes 40mA when used as input? I highly doubt it.
Similarly, the DATA pin on HT1632C, when used as output, can typically source 20mA.
As I said, the library only uses DATA as input.