Which is not a justification for the proof?

Pieces of Right Triangles Similarity Theorem Side-Side-Side Similarity Theorem Substitution Addition Property of Equality

There are no marks to conclude that the sides of the triangle are congruent, it doesn't mean they're not, it just means there is a chance that the side-side-side is out. I am not sure if the AB=C is referring to the angles A, B and C, or if it referring to line segment AB.