"But I'm not like sad, depressed miserable person. I guess sometimes I give off that impression"

In this quote, Edward Furlong is revealing that he is not a naturally unfortunate or depressed person, however sometimes he might discover that way to others. He is acknowledging that his behavior or habits might produce the impression that he is unhappy, despite the fact that might not be the case. This might be due to various reasons such as his body language, tone of voice, or the way he provides himself. Furlong is basically saying that he doesn't want to be viewed as an unpleasant individual, however he understands that in some cases individuals might get that impression from him.