Id imagine the issue isn’t “not showing some people ads”, they probably just got different ads instead if these are the regularly placed ads being talked about.
The article mentions something about this being started by someone who went to Facebook looking for an insurance provider though, so this sounds more like if Amazon didn’t show certain product listings to people of some specific category for one reason or another- those listings are technically advertising a product, but they’re something one actually does want to see, when shopping for something relevant to the listing at least. If, say, some company wanted to offer a product at a discount, but only wanted to offer that discount to a certain category of person for some reason, it’d be pretty scummy of the online retailer to comply and only show other people that product at the more expensive price, or not at all.