I have not misunderstood that setting. "Secure deletion" is not wiping files securely. I wiped junk files using your Disk Cleaner. I was able to find those files intact using Recuva (https://www.piriform.com/recuva).
Secure deletion option in the program actually does not work as its name suggests. I have another program that wipes files in the Recycle Bin securely.