Sync external USB drive to NAS

[Djwad]

Looking for best way to do this.....
I recently bought a Synology NAS and have all my files and folders(pics, Vids, music, docs... Standard home user stuff) transferred over.

I used USB Copy package to copy everything from NAS to a portable Hdd. I will be doing all my organizing, editing, cleaning up of files that are on the portable hdd offsite with my laptop(lots of free time at work.. lol) and bring it home to sync to NAS, probably once a week. On synology forum, Freefilesync was recommended.
I just started messing with it, did some tests. It seems like the external drive folder on the left and the NAS on the right, that "mirror" would do what I need. But I believe when I did compare and then mirrorsync it deleted and created all the files, as in ones I didn't touch on external. From what I recall, after "compare" it said for each file the ones on left were "newer"
Technically they are but I would have thought they were exact copies.

Looking for fastest way for the program to run and deleting and copying every file doesn't seem to be it.
Again, I'm still new at this.. Any suggestions to go about what I want to do?

[xCSxXenon]

Following syncs should not have this problem