Keep in mind that with the 2080, they added raytracing acceleration and tensor cores. Both add area and improve performance of specific user cases, but my guess is that they don't show up in that TFlops number.
I could design you a chip that is nothing but FP32 multipliers and adders that has, theoretically, a ridiculous TFLOPS per mm^2, but it would be next to useless in any real workload.