This is most likely a perspective effect, not a camera fault or unusual optical phenomenon.

Because you were shooting from above the water, the reflected view is not simply a perfect upside-down copy of what you see directly. A reflection in flat water behaves as if your viewpoint were mirrored below the water surface by the same distance as your eye is above it. From that mirrored viewpoint, the nearer part of the hillside can line up differently and block the more distant slope behind it.

So if the skyline is made of a nearer blocky section and a farther sloping section that only appear aligned from your real viewpoint, their positions can separate in the reflection. The nearer land can hide part of the farther land, creating what looks like an abrupt vertical cutoff in the reflected hill.

This effect changes as you move, which matches your observation that the reflection varied across shots taken within a small area. At water level the direct view and reflected perspective would match more closely; from higher up, the mismatch becomes more noticeable.