The reason why it would ask for your information even though he is not a dependent on your return relates to his existing tax position-what is being reported for earned and unearned income and his age.
Keep in mind, if he received any unemployment benefits in 2020, these amounts will be treated as unearned income and may bring him closer to the $2,200 threshold.
The 2020 tax changes reverting back to using the parental rates are much more favorable than the trust and estate rates.
For more information, see: How do I report and pay the Kiddie Tax on my 2020 return?
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