Upon a second look with a fresh mind now, I assume they made the LLM associate certain adjectives (left column) with certain human traits like fat vs thin (right column) in order to determine bias.
For example: the LLM associated peace with thin people and laughter with fat people.
They released a separate PDF of just that figure along with the CSV data: https://static.simonwillison.net/static/2025/fig_3.7.4.pdf
The figure is explained a bit on page 198. It relates to this paper: https://arxiv.org/abs/2402.04105
I don't think they released a data dictionary explaining the different columns though.