As soon as Ancestor Red Cloud finished speaking, the two Western Saints hadn't yet realized the anomaly, but Jiang Chen detected something was amiss first.
It was the two Western Saints who owed Ancestor Red Cloud, not Ancestor Red Cloud who owed them. Since that's the case, why would Ancestor Red Cloud need the approval of the two Western Saints to take control of the Buddha Realm?
He's here to collect a debt; if the two Western Saints don't repay, he can seize it by force.
After all, as long as Ancestor Red Cloud manages to snatch the thing, the two Western Saints, no matter how unwilling in their hearts, can only grudgingly accept.
Who arrives at the door to collect a debt with calm composure? If it were Jiang Chen, and someone owed him and didn't repay, he would also resort to force.
Realizing this, and seeing Ancestor Red Cloud's current attitude, Jiang Chen instantly understood his intentions.