What does a low bilirubin total level mean?

Nothing: The "normal limits" are set so that a few percent of normal folks fall outside. A low total bilirubin is never a problem.

Never a problem: Labs "normal ranges" are set up so that a few percent of people fall below and above the reference range. As a pathologist who's devoted a lifetime to the lab, i can't emphasize too often that patients and doctors must both "look at the person, not the numbers.".