You are of course correct.
The question becomes how? Setting aside the question of who, how were such wonderfully precise vessels and the numerous rectangular boxes and sculptures created? What tools were used to fabricate with such precision?
I would offer time and labor, without directly answering your question.
The above balanced bowl, for instance. Given this balance as the goal, I could see the artist spending large amounts of time, grinding, to achieve it. No two bowls probably have the same dimensions out of thousands, though.