DALI specification: help to understand the physical layer schematic
I think that the terminology is sort of messed up.

They refer to 1 bit as high signal.

They are not referring to the voltage on the wire.

The DALI1_TX and DALI1_RX are active low.

The signals are pulled low by an open collector output for a 1 bit and left floating for a 0 bit (pulled to 3.3V by the pullup resistor).

So the high signal is actually 0V on the wire.