"And those who did wrong kept their private counsels secret," meaning: they committed shirk (polytheism). They would say to one another, keeping that secret among themselves: "Is this," meaning Muhammad, "anything but a human being like yourselves? Will you then yield to sorcery," meaning the Qur'an; i.e., will you believe in it, "while you perceive," that it is sorcery?
Muhammad said: His saying: "And those who did wrong kept their private counsels secret" has two interpretations. It is permissible for "those who did wrong" to be in the nominative case (raf'), meaning: they are the ones who wronged themselves. It is also permissible for the meaning to be: I mean those who did wrong.