«قَرَّرَ الْمَجْلِسُ ذَلِكَ»
The council decided this—that is, its members made the decision.
The word «مَجْلِس» refers to the assembly or place of meeting, whereas the people present are the actual decision-makers. The place or assembly is named for its occupants.
This is mahalliyya. The verb “decided” supplies the context: a room or empty meeting place cannot literally deliberate or choose.