This isn't something specific to AI, but science itself. We know the value of C, but now why the value is C, sure we can point to something like the Lorentz transformation, but we can't and probably won't even be able to explain why it has these particular constants, we just know that we can measure them and they are this.
Science isn't in the business of answering why. A successful scientific theory does two things, A) Makes useful predictions, B) Is correct in its predictions. It'd be wrong to call a NN a scientific theory, but it certainly does make predictions and as these results show, it is correct in its predictions.
Sometime soon, humanity is going to have to come to terms that we will soon (or perhaps already have) enter an age where mankind is not the only source of new knowledge. AI-derived knowledge will only increase as the future unfolds and the analysis of such knowledge will likely become it's own branch of study itself.