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#20
Microsoft does not update the ISO files with every cumulative update they issue. The created on date in your screenshot is 02/13/16. That is the date that MS updated the ISO file. It is reported the ISO file created on that date installs 10586.104.
It doesn't really matter what the minor build number is (.104, .166, etc) because the first cumulative update from Windows Update will take you to the most current minor build number. What matters is the major build number. Going from the 10240 series to the 10586 is more than just a cumulative update - it is a whole Windows 10 upgrade process.
You got the 10240 ISO file the first time because you ran an old version of the Media Creation Tool that you had stored on your computer. The Media Creation Tool exe files are build specific. They will not automatically download the latest ISO. They will download the ISO file that was available when that specific Media Creation Tool exe file was created by Microsoft.