"Were in the middle of harvesting his organs..." He'd be dead by that point.
They can probably remove the corneas before incisions are made for the major organs, but once they make that first incision, those organs come out in a matter of minutes to be placed in sterile containers.
"Had gone into cardiac arrest" meaning his heart stopped. From a drug overdose. Anyone here wanna guess what that means? You got it - CPR. Anyone who knows how to actually do CPR knows that if you do it correctly you are breaking ribs. That's going to hurt like fuck when you wake back up.
When they harvest organs, they aren't just specialized butchers in there. These are surgeons, specifically specializing in organ transplant. The room for error in this specialty is 0. Every modern surgery, regardless of it is organ harvesting or not, will ultimately have a "pause" where everyone goes down the list to make sure everything that needs to be checked is checked.
He likely didn't get to the pause, he probably woke up before that. He was probably being evaluated by the team, and one individual caught something that had been overlooked. The rest of the team spent time to verify, then determined they could actually revive him. This is not a pleasant experience. He would not have been given pain medication beforehand, as he was in for a drug overdose, I could predict it probably wouldn't work anyway.
Whoever went public with this will cause many deaths because of the increase in fear of organ donation.