tip is the dependent variable and "more" is the hypothesis in this study. The hypothesis in this statement is expressed as a prediction, it is an educated guess about what will happen in the study so it is the hypothesis.
Alternatively if reporting the outcome of the study the statement could have said "Patrons in a buffet restaurant did tip more when the server introduced herself by name..." In that case more is simply a confirmed hypothesis, it is still called an hypothesis
Remember, science proceeds by developing hypotheses and submitting them to a test by collecting data. The final criterion of truth for science is does the data confirm the hypothesis.