We are told that angle p is congruent to angle s, angle q is congruent to angle t.
Thus it is an AA similarity theorem because AA similarity theorem states that: If two angles in one triangle are congruent/respectively equal to two angles of another triangle, then the 2 triangles are similar.
For example, if we assume ΔABC and ΔDEF to be two triangles such that ∠A = ∠D and ∠B = ∠E. Then the two triangles are equiangular and thus they are similar by AA.
