How is Handler logic performed on a Deprecated &Message.Publish() call in peoplecode

PeopleTools 8.59 FSCM 9.2

The current syntax used to Create and Publish IntBroker messages are as below

&msg = Createmessage(OPERATION.ServiceOperationName)

%IntBroker.Publish(&msg)

However I noticed there is still some pre 8.4 type code being used in SALES_ORDER_LOAD inbound Flat File (non EDI) utility (FSCM EIP). Here is a snippet of code in related FUNCLIB_EOEIP.FILE_PROC_PC FieldFormula event. I am struggling to understand how this code (highlighted) may still work.

I know that this syntax has been deprecated and exists for backward compatibility. However my question is how will the Integration Broker engine know how to process the message when instantiated and published the old way. I mean no where there is a mention nor associating the message with a service operation. In that case how does the system know how to route the message and what handler to use to subscribe the message.