I've read that some have problems with games updating through Steam even when updates for the game are turned off. One person said it's because when Steam auto updates itself the settings are automatically reverted to game updating.
Anyways, there's a support solution related to it but I'm not sure it works. Have you seen/tried this?
Steam repeatedly updates or verifies game files
To resolve this issue please do the following:
On Windows
Restart Steam
If the issue persists, exit Steam, rename your ClientRegistry.blob, and restart Steam. The ClientRegistry.blob can be found in your Steam installation directory. C:\Program Files\Steam by default.
If the issue still persists, you may have issues with your local Steam files. You may refresh these files without deleting your game files. Please follow this process to refresh your Steam files:
Exit Steam
Navigate to your Steam installation directory. (C:\Program Files\Steam\ by default.)
Delete everything in that directory EXCEPT the following:
steam.exe
steamapps directory (All of Steam's game files are kept here.)
Restart Steam to test the issue
Source:
https://support.steampowered.com/kb_...2971-RUAG-7390