Shaykh Mufid Provides No Proof Against the Imamate of Imam Zayd (as)

I was reading Shaykh Mufid's Al-Irshad. In this book, under the Seerah of Imam Baqir, Shaykh Mufid writes

"Many of the Shi'a believed in his Imamate. The reason for their belief was because of his coming out (in revolt) with the sword calling on support for the one who is acceptable from the family of Muhammad, may God bless him and his family. Therefore they thought that he intended that for himself. However that was not his intention because he knew of the right of his brother, peace be on him, to the Imamate before him, and of his bequest of trusteeship (wasiyya) at his death to Abu Abd Allah (i.e. Ja’far al-Sadiq), peace be on him.

So here from Shaykh Mufid own admission the Shia of the time thought he was an Imam which means he did not declare the Calipate/Imamate of Imam Jafar(as). Also, when you read further he narrates Imam Zayd's (as) meeting with Ummawi ruler Al- Hisham bin Abdul Malik and says

"You are the one who thinks yourself entitled to the caliphate,. Hisham then replies to him and says, “and (you are) the one who hopes for it. But that is not for you. You have no mother. (At least) your mother was only a servant-girl."

Now in a reply, Imam Zayd does not reply by saying there are 12 Calipahs and they are the only one entitled for it. Instead he replies that he is qualified and his mother's lineage does not disqualify him for it. He states

“I do not know anyone greater in rank with God than a prophet whom He has sent,” retorted Zayd. “(Yet such a prophet) was the son of a servant-girl. So if he had been unable to carry out His purpose, He would not have sent him. (That prophet) was Isma'il ibn Ibrahim (Ishmael, son of Abraham), peace be on them. Prophethood is greater in rank with God than the mother of the caliphate, Hisham. Furthermore, a man should not be ignored whose father is the Apostle of God, may God bless him and his family, and who is the son of ‘Ali ibn Abi Talib, peace be on him.”

Nothing in the reply is about the Imamate of 12. In fact the ruler reacts.

Hisham jumped up from his assembly. He summoned his servant and said: “Don't let this man spend the night in my camp.”