The left-hand part of the circuit, up to R5 - D2 - Q2, appear to
be the DALI bus power supply. "There can be only one"...
What is CN4 supposed to connect to, on that unit?
If you are connecting that unit to an existing powered bus, I'd leave out the components after the bridge rectifier through to Q2 etc. and link out the Q2 source and drain connections.
As it's drawn, it looks to really be more a demonstration unit than a fully specified DALI standard unit. I suspect it needs minor mods to be fully DALI compliant.
There is nothing I am aware of in the DALI specs that requires a normal device to contain current limiting.
I can imagine a hypothetical add-on section in a node device to prevent a permanent bus short in case of a device electronics fault, but that would contain a timing network of some sort and the limiter in that design has no time delay, so makes no sense in the context of a node device.
See the Wikipedia article here for some more info: