If you define randomness as less than100% determinism, that doesn't prove anything about the existence of indetermimism, since everything could still be 100% determined. Otoh, thinking that way helpfully gets away from the stumbling block that determinism and indetermimism are metaphysical opposites.

It might be helpful to check out David Bohms "Causality and Chance in Modern Physics" for an account of how the twocan interleave. Among many others.