The spread of misinformation in online social networks (OSN) is a topic of academic research, activist scrutiny, government policy, and generally of public interest. Cutting-edge social science models of OSN-sharing have adopted a (Bayesian) rational analysis approach, grounded in Bayesian decision theory and information theory—and thus, Bayesian epistemology—thereby realizing a de facto (Bayesian) social epistemology of OSN. However, OSN-sharing is a strategic interaction whose choice mathematical model is game theory, not decision theory. And while the issues associated with expressing strategy selection in a game as a single-agent decision problem have been known since the 1980s, they are not addressed by the social science of OSN. We address those issues, propose a solution, and spell out its consequences for academic research, policy-making, and professionals engaged in studying (and countering) the spread of online misinformation.