The Wāsiṭ judge known as Abū Shaybah is Ibrāhīm Abū Shaybah. Al-Nawawī explicitly identifies him as the **grandfather** of the famous transmitters Abū Bakr, ʿUthmān and al-Qāsim, the sons of Muḥammad b. Ibrāhīm Abī Shaybah. The judge and his descendants are distinct individuals; a judgment about their grandfather is not a judgment about the famous Abū Bakr b. Abī Shaybah or his brothers.
Al-Nawawī understands «tear up my letter» as a precaution concerning Shuʿbah’s own written reply, lest its contents reach the criticized person and cause injury or discord. It is not a blanket order to destroy hadith manuscripts.