Should Message Listeners be in System Layer in Mulesoft

I am adding a new flow to my Mulesoft application whose source/starting point is a SalesForce connector that listens to SF Platform events.

I am trying to understand which layer should this message listener be in

The confusion is that,

1. I think as a connector to pull SF data, this listener should be in the system layer
2. On the other hand, should flows be started in the system layer; and then they should call process layer for processing? Shouldn't communication start from experience, then come to process and then system layer ?

TIA

https://www.youtube.com/watch?v=1WjfkyL6OhA : at 5 min 15 seconds

says listeners should be in experience layer