I probably wouldn’t have helped. I would have called the police and an ambulance, and then hoped nobody hit him. I certainly wouldn’t have tried to do anything like direct traffic around the guy. Why?
Here’s the scenario. Mr. Good Samaritan runs out there to try and help. He tries to direct traffic, keeping the victim safe. Except, because he’s out there directing traffic, he causes another accident. Someone is dicking with their radio, not looking ahead. They glance up at the last moment, see this guy standing in the road waving his hands, panic, and jerk the wheel to avoid him. They crash their car, and hurt their neck. Now, Mr. Good Samaritan is getting sued by Mr. Not Looking. Mr. Good Samaritan’s best case scenario is a lot of hassle, and hopefully not too expensive legal bills. Worst case, he ends up owing some jackass their medical bills and car repair, and all he was trying to do was the right thing.
Is it selfish? Sure as hell is. But in a situation like this, you gain no legal immunity by helping, but you definetly expose yourself to significant potential liability. It’s a terrible way to think, I know, but it’s true.