I think this is right. The idea that you would be betting against another person is inessential, an unfortunate distraction arising from the choice of thought experiment. Admittedly it's a natural way to understand the thought experiment, but it's inessential. The experiment could be revised to exlude it. In fact every moment we make decisions whose outcomes depend on things we don't know, and in making those decisions we are therefore in effect gambling. We are surrounded by risks, and our decisions reveal our assessment of those risks.