Hello,
If I understand correctly, "endpoint" means that the disconnect was triggered by the participant's media endpoint. For example, the phone hung up. If you saw this in a participant's row in the timeline, it usually means that that participant hung up their physical phone.
And I think that "peer" means that another participant in the conversation ended the call. For example, if you saw this in the timeline view, "peer" would mean that someone who is not the participant in that timeline row ended the conversation.