Cycle shorts seen as underwear , as per pick n pay

I have bought a pair of cycle shorts from pick n pay princess crossing. When I tried it on, I realized that I would need a smaller size. I then went to pick n pay Flora centre, where ai was told that the cycle shorts was seen as underwear, and cannot be be exchanged. Why was the short between other shorts and long pants, and why was there no notification at all stating that it could not be exchanged?