It is certainly difficult to comprehend how anyone could understand string theory without a solid grasp of the revolution wrought by the impact of probability and statistics on physical theory.
As I alluded to above, advertising “string theory” courses is probably just marketing by the school district. But you’re correct about the impact of probability (as part of the quantum mechanics) and statistical physics in the larger scheme of things. All of that requires way more than AP Calc to get by.