Yes, money is fungible.
You making contributions on behalf of your child is no different than you gifting cash to your child and your child making the contribution deposit. In 2023 an individual can gift up to $17,000 to anyone before needing to file a tax return.
I can see where the use of the word 'match' in the nerdwallet web page can be a bit misleading, but in the same sentence is does say that total contributions can't exceed compensation (which may have already happened if the Roth contributions exceeded net profit reduced by the deductible portion of self-employment taxes).
