I don’t think this is correct. My understanding is that the parent income phaseout for both the qualifying child tax credit (up to $2,000 for dependent children under age 17) and the non-qualifying child tax credit (up to $500 for other dependents) begins at $400k for married filing jointly taxpayers and at $200k for all other filers. This is not low income. Also, the income limit for the actual dependent in claiming the $500 credit appears to be for non-child relatives who are claimed as dependents, and does not apply to dependent children, as pointed out in the article that you provide a link for:
Apparently, these non-child relatives will only qualify for the $500 credit if they have no gross income for the year, because the tax-law language says they cannot have gross income in excess of the dependent exemption deduction amount. For 2018-2025, the dependent exemption deduction is deemed to still exist, but it equals $0.