Bastian was able to map triangle ABC onto triangle A'B'C' using a reflection, rotation, and a dilation. Then Bastian concluded that he was able to map triangle ABC onto triangle A'B'C' using a sequence of rigid transformations and dilations, so the triangles are similar. What error did Bastian make in his conclusion? Bastian used a rotation, so the triangles aren't similar.

Bastian used a combination of similarity transformations, which can produce a non-similar result.

There is no error. This is a correct conclusion.

Bastian used a dilation, which does not preserve similarity.