Clothes, grooming, economic circumstances, physical appearance, youth--all these things impact how people are perceived by others. The first guy looked like a "businessman" -- the second guy looked like a "bum." People were not afraid of the businessman, but they were fearful of the bum.

This is not news. It's sometimes difficult for people to see the humanity in the least of our brethren.

Once he stepped in to help the other guy felt comfortable enough to help. I think you are right about people being fearful of homeless because they are often mentally ill.

if their appearance might indicate they were picked on in school, I feel like the way they were treated shaped their worldview.

They could have had the fake homeless guy fall in crosswalks (!), like suit guy does, where the urgency to help is quicker, they didn't.

They cut the sync audio when they switched to the fake homeless guy so you can't tell if he making less noise or saying anything. For all we know he is saying "I'm okay, I'm okay" or he is saying nothing at all.

Businessman falls in more crowded situations, maybe midtown. Fake homeless guy seems to be on the east side and is always 20 feet from people, except the panhandler.

For both men, when they fall right in front of other people they are helped. When they fall 20 feet away from people they are not.

These videos are staged to create the impression that they are doing some kind of scientific social experiment but there is nothing scientific about this one.

The overwhelming majority of people in the world care about other people.

I was out for lunch in Toronto at Yonge & Dundas when an extremely drunk man staggered around and fell face first into a lane of traffic.
Not one person went to help him.
I stopped, and began to help him up by his coat when another "visually unappealing" man came over to help me with him.
we managed to get him to his feet and slowly guided him back to the sidewalk, and eventually to a wall along a building.
As we were walking him to a safer out of the way spot, I watched as at least 3 people recoiled in fear, and I am not exaggerating.
Their eyes were as big as saucers, mouths agape as if we had just captured the most hideous of creatures and were parading it around for all to see.
Once he was settled at the building, his drinking partner came over and said he would take care of him. I asked if he was sure, and he said he was. The man did appear to not be close to as inebriated as the man we helped, so I moved on.
I will admit, it took me a couple seconds to decide whether to help him, but a quick scan of the situation, fallen into a very busy lane of traffic etc I knew he needed to be helped.