Yes, he will be required to file. Although his overall income is less than $6300, he will be required to file because his income is self-employment. The IRS requires self-employment income to be filed when it is more than $400. Here is an FAQ that helps understand what self-employment is: https://ttlc.intuit.com/replies/4771022
Self-employment income is subject to self-employment tax (basically social security and medicare), which is automatically taken out of an employee's paycheck. But since he was a contractor, he did not have these taxes taken out of his check. This is why he must file, so that the amount of self-employment tax is calculated and paid.
Please note, however, that he is allowed to claim any expense deductions that he had to lower his self-employment tax responsibility. TurboTax will assist you with this.
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