Whether or not it was cramps is for the physio to decide. The umpire isn't a medical professional and won't tell a player they can't have an MTO. They will err on the side of caution and allow the physio to diagnose/treat the player. Can you imagine if someone had actually strained a muscle and the umpire said no, you can't have an MTO because it looks like cramps to me. If you run back the video, she actually says that to Zed when he's having his whinefest. She said, I don't know that it's cramps.
But you can put all of that aside because Zed won the next 2 sets and served for the match in the 5th, but he's a headcase who lost his own physcial form by the end of the match, so continue making excuses for him. The only way this boy will win a slam is if the opponent defaults in the final.