Well, both I guess. 2 Peter 2:1 and this entire chapter is referring to nonbelievers. :)
I thought that might be your passage. Technically he's talking about false teachers but makes a parallel to the false prophets of old. But I think the same principles apply. False teachers likewise have a way of bolstering each other by all repeating the same thing. By the way, the specific reference to this copy-cat phenomenon is in Jeremiah 23:30: "Therefore behold," declares the LORD, "I am against the prophets who
steal from each other words they attribute to Me."
I prefer discussing the prophets as I find them more interesting, and I just read over a passage that suggests the false prophets can sometimes be utterly deceived by a lying spirit allowed by God to delude them, similar to how Pharaoh became utterly deluded. But even here I think this only happens when they have consistently given themselves over to falsehood, and God has finally allowed them to be made an example of, together with a king who must now be made an example of as well.
1 Then the king of Israel gathered the prophets together, about four hundred men, and said unto them, Shall I go against Ramothgilead to battle, or shall I forbear? And they said, Go up; for the Lord shall deliver it into the hand of the king. 7 And Jehoshaphat said, Is there not here a prophet of the Lord besides, that we might enquire of him? 8 And the king of Israel said unto Jehoshaphat, There is yet one man, Micaiah the son of Imlah, by whom we may enquire of the Lord: but I hate him; for he doth not prophesy good concerning me, but evil. And Jehoshaphat said, Let not the king say so. 9 Then the king of Israel called an officer, and said, Hasten hither Micaiah the son of Imlah. 10 And the king of Israel and Jehoshaphat the king of Judah sat each on his throne, having put on their robes, in a void place in the entrance of the gate of Samaria; and all the prophets prophesied before them.
11 And Zedekiah the son of Chenaanah made him horns of iron: and he said, Thus saith the Lord, With these shalt thou push the Syrians, until thou have consumed them. 12 And all the prophets prophesied so, saying, Go up to Ramothgilead, and prosper: for the Lord shall deliver it into the king's hand. 13 And the messenger that was gone to call Micaiah spake unto him, saying, Behold now, the words of the prophets declare good unto the king with one mouth: let thy word, I pray thee, be like the word of one of them, and speak that which is good. 14 And Micaiah said, As the Lord liveth, what the Lord saith unto me, that will I speak.
15 So he came to the king. And the king said unto him, Micaiah, shall we go against Ramothgilead to battle, or shall we forbear? And he answered him, Go, and prosper: for the Lord shall deliver it into the hand of the king. 16 And the king said unto him, How many times shall I adjure thee that thou tell me nothing but that which is true in the name of the Lord? 17 And he said, I saw all Israel scattered upon the hills, as sheep that have not a shepherd: and the Lord said, These have no master: let them return every man to his house in peace. 18 And the king of Israel said unto Jehoshaphat, Did I not tell thee that he would prophesy no good concerning me, but evil? 19 And he said, Hear thou therefore the word of the Lord: I saw the Lord sitting on his throne, and all the host of heaven standing by him on his right hand and on his left. 20 And the Lord said, Who shall persuade Ahab, that he may go up and fall at Ramothgilead? And one said on this manner, and another said on that manner. 21 And there came forth a spirit, and stood before the Lord, and said, I will persuade him. 22 And the Lord said unto him, Wherewith? And he said, I will go forth, and I will be a lying spirit in the mouth of all his prophets. And he said, Thou shalt persuade him, and prevail also: go forth, and do so. 23 Now therefore, behold, the Lord hath put a lying spirit in the mouth of all these thy prophets, and the Lord hath spoken evil concerning thee.
24 But Zedekiah the son of Chenaanah went near, and smote Micaiah on the cheek, and said, Which way went the Spirit of the Lord from me to speak unto thee? 25 And Micaiah said, Behold, thou shalt see in that day, when thou shalt go into an inner chamber to hide thyself. 26 And the king of Israel said, Take Micaiah, and carry him back unto Amon the governor of the city, and to Joash the king's son; 27 And say, Thus saith the king, Put this fellow in the prison, and feed him with bread of affliction and with water of affliction, until I come in peace. 28 And Micaiah said, If thou return at all in peace, the Lord hath not spoken by me. And he said, Hearken, O people, every one of you." (1 Kings 22:1-28)