It's really not so extraordinary, exponential reduction in logical errors when the physical error rate is below a threshold (for certain types of error correcting codes_ is well accepted an both theoretical and computational grounds.

For a rough but well-sourced overview, see Wikipedia: https://en.wikipedia.org/wiki/Threshold_theorem

For a review paper on surface codes, see A. G. Fowler, M. Mariantoni, J. M. Martinis, and A. N. Cleland, “Surface codes: Towards practical large-scale quantum computation,” Phys. Rev. A, vol. 86, no. 3, p. 032324, Sep. 2012, doi: 10.1103/PhysRevA.86.032324.