Your hard disk reached the problematic disk area, which was previously present but not yet "discovered" by the hard disk drive.
This is not rare, problems can remain hidden for very long time (even for years) until the disk drive reads/writes the problematic sectors - when discovered and can result in a quick health degradation.
This is described at Support -> Knowledge Base -> Hard Disk Cases -> Bad sectors:
https://www.hdsentinel.com/hard_disk_ca ... ectors.php
and this is why I always recommend intensive testing (even a new drive) before using it to fill with data:
https://www.hdsentinel.com/faq.php#tests
exactly to reveal such issues long before they can cause damages/data loss - or confirm if the hard disk drive is REALLY 100% perfect.
6% health is very low. Usually such hard disk drives do not work for long time and the status may be enough to get a warranty replacement, so I'd perform a backup of all files/important data as soon as possible and then try to ask for warranty replacement.
Please do not be confused: NOT Windows update caused the LOW HDD HEALTH.
Windows update just performed reads/writes, so the same could happen during any other disk intensive operation:
- copy/move high amount of data on the drive
- save/download additional files
- perform defragmentation and/or antivirus scan
- perform disk testing
These (like the Windows update) may read/write sectors which previously not read/written by the hard disk at all, so these all can reveal problems.