This sounds like a package or plugin that is doing you favours you don't want it to. I'm not aware offhand of any built in feature that would open a file just because you opened something else.
Uninstalling and reinstalling don't have any effect on your settings or installed packages because they're kept in your user directory; if they were in the install directory multiple people using the same computer would be forced to use the same settings .
You can follow the directions at https://www.sublimetext.com/docs/3/revert.html to revert Sublime to a pristine installed state if needed (Note: when it says 'data directory', it's referring to the path itself, even though it says that's where the data directory is contained).
Assuming you're using PackageControl to install third party packages (and that you have any third party packages installed), you can copy the list of installed packages from the Package Control settings to the list of ignored packages in your personal settings to disable them all (except PackageControl itself).
Once you've done that, restart Sublime, verify that the problem is gone, and then slowly enable packages one at a time (you can use PackageControl for this) until you find the one that makes the behaviour come back.
Often just looking at the full list of packages you have installed in this case will spark your memory about the one that might be causing the issue.
If you don't have any third party packages installed, or you do and this doesn't help, the next most likely culprit would be a plugin file that you have installed in your
User package. In that case you'd need to examine each one to see if it looks like it's doing something
on_load or some such.