How can you consider unreliable the narrator of JWJohnson's Autobiography of an ex-colored man?

the reason the narrator of the Autobiography of an Ex-Coloured man is unreliable is simply due to the many instances where the narrator boasts of his "qualities", such as piano playing (eg. where he brings everyone to tears and how his father praises him), learning a new language (speaking better spanish than the south americans), acquiring the 'master' skill of cigar rolling and pro gambling skills