I don't read that paper as backing that claim. At best the paper finds that the mechanism is more complicated than "money transfer from the poor... to the rich". To quote the conclusion directly:
"Notably, our results are not driven by income, as they hold within the sub-samples of low-, middle- and high-income individuals. In particular, high-FICO high-income consumers benefit the most from reward credit cards, but they do so at the expense of low-FICO high-income consumers. While credit card rewards are often framed as a “reverse Robin Hood” mechanism in which the poor subsidize the rich, our results show that this explanation is at best incomplete."
"Notably, our results are not driven by income, as they hold within the sub-samples of low-, middle- and high-income individuals. In particular, high-FICO high-income consumers benefit the most from reward credit cards, but they do so at the expense of low-FICO high-income consumers. While credit card rewards are often framed as a “reverse Robin Hood” mechanism in which the poor subsidize the rich, our results show that this explanation is at best incomplete."