Collective speech attribution does not imply one identical belief held by every group. Several parties may be grouped by a plural verb while the actual content of their claims differs or even conflicts.
In the verse, qālū provides a collective introduction; it does not prove that each party pronounced the same combined formula. The later labels distinguish the claims attributable to each group.
Whenever a collective reporting verb is followed by multiple statements, the analyst must ask whether every statement belongs to the whole body or whether the claims distribute across distinct members. This question identifies collective laff.