No, the Account Owner cannot see the details of a Coach's discussion with a Participant. Here's an example of what the Account Owner would see: 
 
1) The Account Owner would see a headline/title of the Coach/Participant discussion. Below is an example. 
 
 
2) If the Account Owner clicks on the discussion to try to view the content of the discussion, they won't be allowed in and will get the following screen indicating that they don't have access to the page.