This question implies that Wiesel took certain creative license in how he chose to portray his experiences of the Holocaust and that the literary presentation of his memories does not correspond with reality. The act of literary creation is of course one that does involve conscious ordering of events and a certain amount of shaping of those events for a specific purpose and to convey a specific message, and it is clear that Wiesel would have gone through this process to a certain extent.
However, at the same time, reading the book, it becomes clear that Wiesel has not felt it necessary to add or stray too far from reality in order to create his memoir. Significantly, what happened to him during the Holocaust needed no addition in order to convey the true horror of his message about what man is capable of doing to his fellow man. Throughout, his first person account of what he witnessed and experienced is enough in itself to convey the kind of feelings and emotions that he wants to show. Consider the following example, coming straight after the hanging of the boy that has such a profound impact on the author:
I watched other hangings. I never saw a single victim weep. These withered bodies had long forgotten the bitter taste of tears.
The first person account is open and honest, and although there are choices made in terms of presentation of a memoir, it is clear that the account of Eli in this text is the same truthful account as that of the author as he writes about his past and tries to make sense of it and what it means for both himself and for humanity.