Seems more likely that they tried this as a desperate last attempt when things were already going down the drain.

I somehow link this practice to the Brave browser, but I'm not sure about it. Does anyone know more about it?

Brave blocks ads on pages you browse, and then sends ad notifications to user who opt into their earning program (disabled by default). It pays them in BAT, a crypto coin they developed. If you want to, you can use these earnings to contribute to sites who have signed up to accept their crypto coin.

It does not replace ads on pages with it's own.

He's talking about Adblock Plus, they whitelist "acceptable ads" and vendors need to pay them to be classified as such.

Apparently Adblock Plus makes enough money from that practice that they managed to buy flattr in 2017.