Concept:
Topology errors are mistakes in the spatial relationships between GIS features.
Common topology errors include overshoots, undershoots (dangles), and spikes.
A buffer is not an error—it is a GIS analysis tool.
Step 1: Understand each option.
• Overshoot: Line extends beyond its intended intersection.
• Dangle: Line endpoint remains unconnected.
• Spike: Small unwanted projection created during digitization.
• Buffer: Creates zones at a specified distance around features.
Step 2: Identify the non-error.
A buffer is a spatial analysis operation rather than a topology error.
Hence,
\[
\boxed{\text{Buffer is not a GIS topology error.}}
\]
Therefore, the correct option is
\[
\boxed{(C).}
\]