As I recall – and I will look this up later to check my recollection – the first three things to check for with a person who has passed out and collapsed (that is, fainted or for whatever reason become unconscious) is to check – in this order – Breathing, Bleeding and Broken.
Breathing should be obvious. A person who isn’t breathing will die within a few minutes.
Bleeding is next, because with heavy bleeding a person can also die in short order, not much longer than it would take them to die from lack of oxygen, that is.
Broken bones cause pain, obviously, and can lead to collapse if the bone (or joint) is one that is being used to support a person’s weight. And compound fractures – those where the bone is broken so badly that one or both ends protrude from the skin – obviously carry additional risk from bleeding and infection. But those wounds are not – usually – life-threatening.
So the first thing to do when someone passes out – and again, this is from memory – is to check if they are at all responsive while at the same time checking for breathing. If the person is breathing and not bleeding, whether conscious or not, then in general the best thing to do is to protect them from traffic (foot and vehicle traffic, obviously) and leave them alone. The caveat is that if the place where the victim has collapsed is dangerous because of heat, cold, toxicity, lack of oxygen itself, fire or flood, etc. – or is in the middle of a roadway – then it may be necessary to move the person to a safer area.
In the case of the person you witnessed, where it’s apparently not a life-threatening emergency, then getting the person to a quiet place where he or she can sit and rest, maybe take some water and be comfortable, is best.