I think I can guess why. I feel that for each question that the course author prepares, they also have to prepare multiple answers for them, so as to catch the multiple possible ways a user might answer the question in an acceptable manner.
So here, the question was: "The board"
So both "คณะกรรมการ" (committee / board) and "กระดาน" (a physical board, e.g., a blackboard) are acceptable.
That leaves another question open. Why is it that when we visit these sentence posts in forums that the heading only makes one translation answer visible? E.g., in this case, it shows:
- "The board"
- Translation: คณะกรรมการ
When a user sees this, I can understand why they would assume that the answer shown here is the 'correct' answer. Perhaps Duolingo requires the course author to select a single answer to be displayed here, out of all the 'possible' answers. So they select one which they consider to be the most correct.