A "user" is defined in one of two ways, for named users on restricted datasets, there is a specific user login , meaning individual users can be tracked for restricted datasets. However, for open datasets the only way to identify the user is by their IP address.
This does mean that a "user" may not correspond to one person. For example, a user may login at home to access data, then at different buildings at an academic institute, all of which would be identified as different users. Additionally, some users appear to be using torrent software to spread the download across multiple computers/ IPs, all of which will be identified as "users", even though only one person might be interested in the data.
If you only wish to examine statistics for all/ named/ anonmymous users they can be selected using the "Users" dropdown menu.