That was in-camera underexposure. When doing handheld night shots, I routinely compensate by -1EV (usual street shots) to avoid overexposing the highlights, and to keep the sky or unlit parts reasonably dark. The setting gets increased to -2EV in darker places. At post-processing stage, I then need minor corrections, if any. The shadows remain reasonably noise-free with the Df, or even the D800 after sampling down. In such way, I also avoid lowering the speed, which is generally 1/FL (the "neutral" auto ISO setting).
