The admin guide has a section devoted to the Site Analysis tab and basically summarizes the actions of the reports:
Monitoring Site Usage
You can monitor the number of licensed users that have connected to an ALM site over a selected period of time. You can analyze the usage level of each module and extension, and track the peak usage level in the current month. The data can be displayed in line graphs or data grids. In addition, you can filter records by projects, users, or license type, and save data to a file.
So this is a cumulative running total of the licensed users connecting to ALM. It also takes into account any connection that is made through a third party application or otherwise (such as UFT, Synchronizer, REST or OTA api calls, etc) that establishes a connection and uses a license. IOt cumulatively totals these and it isn't necessarily tallying individual user connections but any individual licensed connection (so a log out, release of that user license, then log back in later by the same user that gains a license again would in actuality be two connections).
I hope this help[s in your understanding of the data.