You should read more carefully. If you follow the link in that thread, it gives you step-by-step instructions on how to fix it. It doesn't matter if you've cloned your HD or not. The issue is duplicate entries in the "Open With" menu, regardless of how it happened.
If you're not handy with Terminal commands and if you have Onyx, you can rebuild the LaunchServices database:
Open the Automation panel or open the Maintenance panel and select the Rebuild tab...
Check the "LaunchServices" case and uncheck the other cases.