When Windows is presenting this dialog, how does it compare which of those two modified dates is "newer?"
At first, I thought Windows was comparing the Date Created attribute and using the result of this comparison to label one or the other "(newer)." (If a file was copied in to a particular location, it may have the creation date of when the copy happened, rather than the original creation date of the file.) However, reproducing it with another file, the result of which is "newer" seems to be the opposite:
It is shown for either Copy or Move:
And for background, the file in test2 is a previously made copy of the file in test1.