I'm trying to see this from the perspective of the car owner / other occupants. They've never met this guy. He smokes some weed, has a bad reaction, and says he wants to get out of the car. They try to reason with him and say, you're okay, it'll be fine.
But he says he's got a knife, he's a demon, he's going to wreck the car. He's going crazy and he's scaring them.
So they pull over to the side, he jumps out, runs across the highway, jumps the barrier and disappears. They wait for a little while to see if he comes back for his backpack/phone, but he doesn't. So they leave them by the side of the road in case he comes back for them. They call his mum, call his grandpa to tell them what happened. They probably figure he'll make his own way home once he calms down.
Giovani is 18 years old, he's an adult. They don't know him. He's threatened them and left. They did the right thing by calling his mum and grandpa to let them know, but they can't have possibly predicted that Giovani would sprint down an embankment into a in a knee deep pond and die there.
These guys have to live with all the "What ifs". What if we'd talked him down. What if we'd let him out somewhere else. What if we'd called 911. What if we'd chased after him etc.
I feel bad for them, but I don't blame them.
What happened was a tragedy, but it's not their fault.