You're right, these images are rendered with path tracing (I do also have a Whitted integrator). However tray_rust is a ray tracer in the general sense where it refers to a family of methods that all involve tracing rays to render an image, eg. Whitted recursive ray tracing, Path tracing, Bidirectional path tracing, Photon mapping, Metropolis light transport, Vertex Connection and Merging, etc. (since I hope to implement some of these methods as well!).