College Student's 1099-NEC earnings showing as unearned income

My full time college student worked as a construction laborer last summer.  His $5390 in earnings were reported on a 1099-NEC form.  I understand he will have to pay self-employment taxes since no taxes were taken out of his income.  However, TurboTax keeps prompting us to complete Form 8615 referencing his earnings as "unearned income".  Why?