By default we see User Mentions pivoted on Mentioned Member Name in the "Top Mentioned Members" visual on "The Network" page. This results in a visual that displays the number of mentions that a user has received. For this measure, the row context created by the Mentioned Member Name column is very important because the same measure can represent both sides of the mention depending on the pivot column.
We can demonstrate this by comparing two charts the first on the left is User Mentions by Mentioned 'Users' Mentioned Member Name, and the second chart is User Mentions by 'Users' Member Name. In example image 1 we can see that the total Number of Mentions are equal but the value of Mentions is different. The first chart representing the default case, total mentions received by that user, the second chart displaying the total mentions made by that user.
We can further this understanding by filtering to Dean Swann in the first chart. Now we can see that his User Mentions = Total User Mentions by Member Name in the right chart. Thus the right chart shows the number of mentions made by those users who mentioned Dean 506 times.