An opponent stops to help the cramping player. To take advantage of that by playing with an injured (only cramping) player is pathetic

Why? The injured player was still on the ground. The ball was not in play. The referee should have indicated a ceremonial restart and asked for attention for the injured player. This wasn't bang-bang - there was quite a bit of time between the whistle and the restart.

On a side note, I didn't keep watching but I assume the 'injured' player was just fine.