Gu Xijiu was the one who had instructed Gu Canmo to act in that manner. She wanted to have the questions during the ceremony to profess her undivided love to Di Fuyi in front of everyone. Agreeing to all the conditions in the vow was equal to swearing an oath to heaven and earth. No one was allowed to go against his or her words once the oath was made.
Gu Canmo also realized that it was not exactly a propitious thing to say. However, The Lord was, after all, immortal. What he said would not do any harm to The Lord at all, so he did exactly what Gu Xijiu told him to.
Di Fuyi's expression changed when he heard the vows. He looked at Gu Xijiu and communicated with her through directed audio. "Xijiu!"
Once she agreed to the vows, the oath would be immediately established. After he was gone, she would have to live alone for tens of thousands of years until death came upon her. He would not allow her to commit herself into something so foolish.