I'd say 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 just that.
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 quite 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 guys stepping in front of Jack, hiding him 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 that 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.