The Find duplicates is an advisory screen report not an absolute as there are many factors that can lead to false positives.
It works best if you have at least 3 data items, e.g. Name, DOB, POB and preferably parents as well.
The report encourages you to examine each person (compare) and consider additional facts before considering a merge from this report.
I find that if I know I have duplicate entries it is better to use the Merge two specific individuals in the People Menu.
I would encourage the use of a practice or dummy file to practice using the find duplicates and merge two specific individuals as merging can make big and sometimes unintended changes to your file.
Having good backups before you merge is recommended, and in fact FTM offers to do this before most merges