Being more in free diving than SCUBA you are always by yourself and normally out of sight from any boat. Good or bad if your spearfishing you normally don't want to be around anyone else. Generally you will be dropped off in the current and you will say I'm going with the current and pick me up in about an hour down current. Years ago I was on a dive boat after a competition off the coast of the Florida Keys. I was the only free diver and talked my way on board so I could see the famous Statute of Christ underwater. The boat was filled with beginning SCUBA divers from Minnesota who had never been in the ocean before. The current was ripping as you could see from the anchor line. Being just with fins and mask I was in first. I knew that the others with all their gear would be in trouble. Sure enough, just as I was beginning to get ahead of the bow I heard the dive master yelling for everyone to get back in the boat. Too late for the Minnesota people as they were now spread out all over the ocean and down current for at least a mile. The rest of the day we spent picking them up. Never did get to see the Statute of Christ.
So these things do happen. Not sure what really took place in that movie but the dive master or skipper is supposed to take a count before and after a dive before moving to another location or simply going home. I have an acquaintance who lost his license for failing to do just that and he left a diver overnight who was eventually rescued the next morning.