Random bystanders helping Reacher out

I'd say that whoever added this scene, may it be the screenwriter, producer, director, author of the book or someone else, was just looking for a more or less original and clever way of ending the car chase and letting Jack Reacher get away. And, by having him jump out of the car when no one sees and then just letting it continue down the road while he's heading in some other direction by foot (in this case to a crowded bus stop) they managed to do just that.

I have actually read the book now and there are no car chases at all in it, so the chase and the scene(s) right after were definitely added afterwards.
Fun Fact: The notable bathroom fighting scene was also just a movie addition.

When it comes to the reactions of the people already at the bus stop, I don't think there's anything out of the ordinary. Sure, they could've had some people run off, but, when you see some guy getting chased by a dozen police cars and he walks over and stands right next to you, I think most people would just stand there quietly and hope that the police sees him. Not many people would try to get the attention of the police since that would most likely also get the attention of the perpetrator, possibly leading to them getting hurt or maybe even killed.

The two men who hid Jack from the police are just there as comedic relief. But, I wouldn't say that it's totally unrealistic. Without having any kind of statistics backing me up on this, I'd say that people who have been arrested before, and especially people that have been unjustifiably arrested (which, sadly, happens sometimes, and especially to non-Caucasian citizens like the two gentlemen in the movie) would help others hide from the police, as long as it's not too much trouble.

I like to think that they decided to not turn him in because Americans often are rooting for the person being chased in high speed pursuits. Anecdotally, Americans seem more exposed to high speed chases on the news and on live television, and honestly, it doesn't seem unlikely that a group of people would not report someone who simply walked away from a high speed chase, because it rarely happens that the pursued suspect escapes and it is often assumed that the police are overreacting.

Its one of the weaknesses of having Tom Cruise play Reacher. Imagine yourself in the same situation except a 6.5' monster is standing next to you. Yea you'll give him your hat.

Add to this the stereotyped inner city attitude towards cops and it is very realistic.