If he receives a Form 1099-NEC, he is considered self-employed for tax purposes. As a self-employed person, you need to report all the money you earn. If you make $400 or more, you'll likely need to pay self-employment tax. You can find more information in this TurboTax Help Article.
If the income is actually from a hobby, it should have been reported on Form 1099-MISC, not Form 1099-NEC. He would still need to file a tax return and report his income, but he wouldn't have to pay self-employment tax.
