Was Guru Nakan Sahib a Muslim?

Iv heard that Guru Nanak Ji was a muslim and apparantly his real name was abdul majeed? is this true? im a muslim and i respect him alot but someone told me that he grew up around muslims, before him there was no sikhism and he kept a beard, wore a pag(turban)-which is a sunnah and he also had a Juba inscribed with quranic verses and he prayed 5 times a day and he also went to mecca when only muslims can enter mecca? so im not sure.