That is correct - it repairs the volume and not what is causing a boot problem.
Are you helping to try and resolve this error ?
Does the machine have any peripherals plugged in like an USB HDD or anything else other than a mouse - and it could even be a mouse that is the cause of this.
Sometimes this can be a one time glitch and doesn't reappear on the next boot, but can the machine be booted into the advanced boot options by pressing 0 or F8 as it is switched on.
Safe Mode would be a wise option so as to back up any personal stuff.
In the advanced boot options there is an option for Last Known Good Configuration which could take it back to the last good config where it will boot without error.
Other options in there is Repair your computer where you can navigate to the Recovery Environment and select Startup Repair to see if that can do anything - it's advised to run that up to three times if at first it doesn't resolve.
Next is to select the Command Prompt and enter rstrui.exe which will get you to the restore points to see if any of those will help.
Also from the Command Prompt, enter these cmds -
bcdedit |find "osdevice" and using whichever partition letter, use that instead of the x I have used in this cmd - chkdsk x: /r
That is a Pipe symbol before find and is the uppercase of \
Running a chkdsk in this mode will negate the need for the volume to be dismounted through a reboot and its report will be on screen as it completes.
Generally you are looking to see if it reports any KBs in bad sectors, but it may also repair the file structure which could be the cause.
If it reports KBs in bad sectors then the owner should back up anything important straight away before complete HDD failure.
Anyway, if you are working on it, then let us know how you get on with those suggestions or pass them onto the owner.