You can find this information on the log tab of the auto-update page. You'll find it at /autoupdate.htm?tabid=2# . Assuming each user has a unique login, you can determine if it was manual or automatic.
The default time for auto-updates is 1AM. I checked my own logs and there appears to be a difference between auto and manual:
Disclaimer: The information in the Paessler Knowledge Base comes without warranty of any kind. Use at your own risk. Before applying any instructions please exercise proper system administrator housekeeping. You must make sure that a proper backup of all your data is available.