LISTENER setup in a cluster environment

Hello all

We have a question on the basics of how the LISTENER works in a RAC / High Availability setup

So basically in a single / non OHAS database setup we setup database and we create a listener

so we have 2 set of 2 node set. #1) 2 node RAC - BOSTON and #2) 2 node RAC- NY

Both clusters are using SCAN listeners

BOSTON has few RAC databases running and one of those database is QADB

on node-1 of NY cluster we configured a single instance standby and then added the standby database to the cluster using srvctl add database and srvctl add instance and we noticed that we did not configure any LISTENER for that standby and yet the primary nodes are able to ship the logs out. So we are trying to understand how does that work? I mean we did not configured a listener for standby and yet primary db is able to ship the logs out