I also wondered why Thoth was voting for a 7 year old post. Then I remembered that Thoth is supposed to be part of your extended reward concept. Did I understand that correctly?

Yes, it is part of the extended reward concept. Thoth doesn't actually vote for the inactive posts, but it highlights them in its own post and then shares beneficiary rewards with the authors that it finds. In this manner, quality posts can get resurfaced multiple times across the years and they can keep generating rewards for the author each time it happens.