Answer: because his friend was breathing and did not need chest compressions.
Step-by-step explanation:
Based on the information given, the reason why the paramedics were surprised to see Greg performing chest compressions on his friend is because his friend was breathing and did not need chest compressions.
Chest compression is done for someone who has stopped breathing and not someone whom is still breathing. In such case, one will use the hands to push down the chest of the person whom stopped breathing hard and fast.