Good Samaritan Nearly Causes Accident

This is dashcam footage of a motorist nearly T-Boning a car crossing traffic. You can see that the car proceeds down the right side of backed-up traffic. It appears that he has the intention of going straight past the intersection since he has no signal on when suddenly a car darts out in front of him. Brake lights go on and a collision is nearly avoided. Cars appear to come within inches of each other from camera’s perspective. It could have been that someone waved the car in to let them through. I have seen this before. Don't trust traffic control direction from a stranger! If something had happened, who’s fault would it have been?