Nephew (Dependent/Student) made less than $9,000 and Turbo Tax shows he owes over $2,000 Federal Tax?

My nephew is a full-time student. He is a dependent. He made a little over $400 (they took out federal tax) and received unemployment pay a little over $8,000 (only took out $30 federal tax). I completed his return as a dependent and after I entered his parents' taxable income Turbo Tax shows he owes a little over $2,000? How can this be if his total income is under $9,000?  Otherwise prior to entering his parents taxable income he only owed a little over $700.