Line-state is the user's status in the cloud PBX. This is pushed one-way from the cloud PBX to Teams.
Teams Connect Line-state

The correct status at all times
Teams Connect Line-state is our slightly simpler solution for those who don't need the full-fledged Teams integration.
With Teams Connect Line-state, you get access to our Teams app, Teams Connect. You still answer calls on your mobile or softphone, but with the app installed, you can set the mapping and line-state. This ensures that you always display the correct status in both the PBX and Teams, making it easier for colleagues and customers to reach you.
Perhaps not all employees have a use for the entire Teams package, or maybe you want to test Teams a bit before fully committing – in that case, Teams Connect Line-state is perfect!
Try Teams Connect Line-state
What's the difference between line-state and referral?
Line-state
Presence
Presence refers to the user's status based on activity within Teams. The user's presence then updates the activity in the PBX.