Or read his lectures on physics if you want a better understanding, his diagrams and thought experiments and perspectives tend to be very physically accessible imo

The photon can take any possible path, the likelihood that it will take a given path is dictated by some complex path integral, it tends towards the "shortest" path but can take others due to uncertainty.

Ultimately all the path integral does is to show likelihoods of paths, not which path will be taken at any one moment.

Edit: this diagram could also just be shoeing that while a surface may appear "flat" it is microscopically far from it