Bhai Bholu Tiwari was a dedicated Sikh of the time of Guru Arjan Sahib. Once he asked Guru Sahib who was the Guru of Guru Nanak Sahib. Guru Sahib told him that the Almighty was the Guru of Guru Nanak Sahib. When Guru Angad Sahib was installed as Second Nanak, Guru Nanak Sahib bowed before him (Guru Angad Sahib) to confirm the succession. It did not mean that Guru Angad Sahib had become Guru of Guru Nanak Sahib.
(Dr Harjinder Singh Dilgeer)