TurboTax uses parts of your dependent's college expenses to claim the Tuition credit. That reduces the amount that can be used to claim the  529 earnings, shown on the 1099-Q, as being totally tax free.

For more detail, see:

 https://ttlc.intuit.com/questions/3742999-i-entered-my-1099-q-and-my-1098-t-to-show-i-used-the-money...

If your income is too high to be eligible for a tuition credit, see this TurboTax FAQ for a work-around: https://ttlc.intuit.com/questions/4451709-why-is-the-529-distribution-from-my-1099-q-showing-up-as-t...