That's right.
Han Yi's first sword strike was aimed at the Demon Ape Great Sage, whose speed, thanks to the eighth-ranked Green Reed Sword, far surpassed the Demon Ape Great Sage's reaction. Although the Great Sage perceived the fatal danger, his body was completely unable to respond in time.
By the time the Camelopard Great Sovereign looked over, he saw the Green Reed Sword piercing through the back of the Demon Ape Great Sage. His Demon Spirit was also headed towards destruction under this sword strike, and unless the Ancestor intervened, it would be difficult to save him.
This spatial seal even prevented the Ancestor from perceiving what was happening inside for the time being.
Moreover, if a trap like this one targeting Han Yi was set, even the Ancestor of Donghuang Evil Court would have to get involved, it would be considered bullying. If the Age Candle sought revenge, and the Ancestor made a move, all these Demon Monarchs and Demon Venerables would face death.