It is important to identify the way in which the account that Humbert offers the reader of his life is necessarily partial and fragmented, and as much as he seeks to offer an accurate and honest portrayal of his own actions, thoughts and feelings, it is clear that only the most naive reader would be willing to trust his version of events in their entirety. The encounter with Jack Humbertson, which occurs in Part 2, Chapter 26, does seem to be one of the many examples of how Humbert's distorted view of events is not entirely reliable. Note the way that Humbert himself freely admits that during this period of his life he drank copious amounts, therefore impacting his perception of what was really happening.
In fact, the theme of appearances and reality is something that runs throughout the entire book, and can be seen to manifest itself yet again in this hotel room encounter. Often Humbert is taken in by appearances, or argues himself into a position where he cannot accept reality, such as when he insists on Lolita being an innocent, as this is part of his desire for her, which means he is intentionally blind to the way she turns into a "cruel manipulator" and ensures that he plays the role of both victimiser but also victim because of the way he is enslaved to his passion for her. The reference to Jack Humbertson therefore clearly suggests that this could be a result of Humbert's overwraught, drunken state, and is not to be trusted.