Yes his point is more general than physics but that's not the point! He's not closing off explanations of related issues in reality. He's closing off methods of weak evidence. He's closing off classes of evidence, not evaluations of expected probabilities. Maybe expanding his example will make this more clear: If his example were equivalent to yours, instead of closing off Kelvin's opinion, you'd be closing off whether or not the Wright Brothers had built an air tunnel. See the difference?