ציטירנדיקער פּירוש אויף ויקרא 4:14

If the court ruled and one of them knew that they had erred and said to the others, “You are making a mistake”, or if the mufla of the court was not there, or if one of them was a proselyte or a mamzer or a nathin or an elder who did not have children, they are exempt, for it says here (Lev 4:13) “congregation” and it says later on (Num 35:24) “congregation”; just as the “congregation” further on must be fit to issue rulings, so too the “congregation” mentioned here must be fit to issue rulings
If the court issued a [wrong] decision unwittingly and all the people acted unwittingly, they bring a bull. This first section is the classic case in which the court must bring the bull as a sin-offering (mentioned in Lev 4:14).

They bring a bull – It says in Leviticus that the congregation sacrifices a bull.

Introduction In the previous mishnah we learned that if the court issued an errant ruling and everyone acted erroneously in accord with that ruling they bring a bull, as it says in Leviticus 4:14, “The congregation shall offer a bull of the herd as a sin offering.” Our mishnah discusses who the “congregation” is that brings the bull. Throughout this mishnah we will read that there is a distinction made between sins involving idol worship and all other sins. In the introduction to the tractate I explained that the rabbis understood Leviticus 4 as referring to regular sins and Numbers 15:22-29 as referring to idol worship. If the sin was idol worship, then the congregation brings a bull and a goat (Numbers 15:24).

to atone for all Israel for they had sinned by [practicing] idolatry. The king said as follows: “Let the burnt offerings and the sin offerings be for all Israel.” In the section שְׁלַח (Num. 16:24) it is written: “the entire congregation shall offer up one bull, etc.,” and it is written: (Lev 4:14): “and the congregation shall bring a young bull for a sin offering,” and here it is written that they brought seven bulls, rams, lambs, and kids! This was a temporary ruling.