If it was reported on 1099-NEC, it MUST be reported as Self-Employment income.
The IRS brought back Form 1099-NEC to avoid confusion, it cannot be reported any other way.
Part of the reason is that the Payer, in your case the Parent Company, does not withhold FICA tax (your Social Security and Medicare Tax) and the only other way that can be collected is through Self-Employment tax.
Self-Employment tax is both halves of the tax (Employer and Employee portion) however you also get a credit for the Employer's half that you pay.
It does seem like a burden for you to report the bonus this way, but unless they included it on your W-2, it's your only option.
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