The output mentions sleep, I would take that to mean that at the end of the day he closes his laptop and it then goes to sleep. In the morning he opens it back up and finds that he’s been logged out, which I would surmise means it rebooted.
To add some detail to what “updated your system” means, it means have you installed updates either via terminal (sudo apt update and sudo apt upgrade or sudo apt full-upgrade) or via the software manager?
this is entering some kind of standby / hibernate mode
How are you determining that you have been logged out? Bear in mind that good security practice often means configuring a computer that has entered standby / hibernate to require the username and password in order to return to normal state - and coming out of a locked (but not standby / hibernate) state also requires the username and password.
It is also possible that something has ‘power saved’ and there is a bug so that it is not handled correctly on one or both of the transitions.
So you definitely need to investigate your power management settings.
Does it make any difference if you don’t close the lid? i.e. let it power save but don’t have the ‘lid close’ event?