I can maybe shed some light on the original question (speculation).
This may be a simplification by EasyEquities (likely in agreement with SARS) in order that people pay the appropriate tax on US dividends.
Ordinarily, one would report foreign dividends at an inclusion rate of 20/45, less tax paid as a rebate (limited, IIRC, to the tax due on the foreign dividends).
Anyway, the effect of this is that 45% rate taxpayers would then be paying an additional 5% to SARS on top of the 15% withheld by EE and paid to the IRS (which makes it equal to local div tax of 20%). However, the Double Tax Agreement between the US and South Africa strictly limits dividends tax in total to no more than 15%.
Therefore, unless in some edge cases where there is no withholding on a US dividend, the appropriate dividend tax has already been paid by EE.
Therefore, you would get the correct tax due by reporting them as local dividends else instead overpay (if you're a 36%+ tax payer) if you report them as foreign dividends, unless you make a compensation elsewhere in your return. 31%- taxpayers it wouldn't make a difference.