That is for W2 income and interest & dividends. For self employment income you have to file for only $400. You won't owe any income tax on it but will owe self employment tax.
Filing requirements for a dependent. The 3rd bullet point.
https://ttlc.intuit.com/community/children-dependents/help/do-i-need-to-file-my-own-taxes-if-i-m-a-d...
See IRS 501 page 5 Table 3 Other Stituations when you must file a return.
#3 You had net earnings from self-employment of at least $400.
https://www.irs.gov/pub/irs-pdf/p501.pdf
