While the general gist of your argument is right, I think there are some non-trivial ways to overfit. There are some 25 constants in the standard model apparently that describe the world around us to enormous precision. This is so little information that of course the trivial 'overfitting by encoding observations directly' will fail, but we could still be overfitting by having an excess number of variables: perhaps there's really some mechanism in neutrino physics that explains neutrino oscillation without needing some constants to describe how it really happens. This might in turn boost tremendously our predictive precision for neutrino oscillation to match the precision of the other more fundamental variables in the model, for example. But I think you're right that it's so little data that we have some strong information theoretic guarantees that at least the model will have predictive power matching the precision of previous measurements.
