Unearned Income

Good morning.  I am working on my son's taxes and have came across something that has me puzzled.  He was 23 years old in 2020 and a student for at least 5 months while in a graduate program.  He coached baseball in 2020 and received a 1099-NEC.  When I place all information into Turbo Tax as instructed, I keep getting that this is unearned income and he has to place my information as the parent.  My question is why would this be unearned income as it was earned for coaching.  From everything I read unearned income is for interest, capital gains, etc.  Any help or insight you can provide would be greatly appreciated.