UART_DEFAULT_CONFIG_BAUDRATE is defined as 30801920?

In nRF5_SDK_15.0.0_a53641a code, there's such definition:

#define UART_DEFAULT_CONFIG_BAUDRATE 30801920

Which means about 30.8 Mbps.

But in page 345 of nRF52832's Product Specification V1.4, you can see the maxim speed of UARTE32 is 1 Mbps.

This don't make sense, What's the matter?