"I don't know much about him; never heard him say more than nope or yup"

This quote by Dashiell Hammett implies that the individual being described is someone who is not really talkative. The speaker has not heard the person state far more than "nope" or "yup," which suggests that the person is not very communicative. This could be interpreted as a sign of shyness or an absence of interest in talking. It might likewise signify disinterest in the speaker or the subjects being talked about. The speaker's absence of understanding about the individual could likewise be a sign of the person's absence of presence in the speaker's life. This could be due to the person's shy nature or simply because the speaker and the person do not have much of a relationship. Whatever the case, the quote indicates that the person is not very talkative which the speaker does not know much about them.