Do Barbarians not count as a Civilization for theming bonuses?

I have the Uffizi which has a theming bonus of all Art from the same Era and Civilization.

As seen below I have three from the Barbarians all from the Ancient Era and I am not getting the theming bonus.

So

  1. Am I doing something wrong?
  2. Are Barbarians not a Civilization? If not what would be the point of getting Barbarian artifacts over random civilization artifacts?
  3. Is this a bug?

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Your problem is not that barbarians aren't a civilization, but that you're not displaying art.

Art specifically refers to the paintings produced by a Great Artist, and not the Artifacts recovered by your archaeologists.