Is it normal to want to yell at strangers when they behave badly?

so i'm buying a soda at the grocery tonight and there is an unusually long line bc its so late and there's only one checker. This clearly homeless guy has got a full cart of random stuff (vodka, flowers, strange combination of other food) and he's talking to the manager, and the manager has him cut in the line.
Basically, he's got a huge cart of stuff, and most of us only have a few items. We're all really annoyed, but one by one, he's like, oh, you can go ahead of me, are you in a hurry. When it gets to me, he tells me that He was in line earlier, and had to leave the line bc someone got in a fight. doesn't really make alot of sense, but i also got the sense the guy had a mental illness.
So, he lets me in front of him, and the people behind me get upset. It's a husband and wife, that clearly have quite a bit of money, they are very well dressed. I am facing forward, and can't see anything.
But this is what I HEAR: the guy in the suit says to the homeless guy, "are you cutting in front of me?" Before the homeless guy even has a chance to respond, he goes over to him, stands really close and starts call him a piece of shit, and says other things i cant hear bc he's talking under his breath. The homeless guy starts yelling at him. "are you threatening me? I'll get security over here! Is that your wife I'm not going to say what I should right in front of your nice beautiful wife!" The guy int the suit is now really getting in the homeless guy's face, and his wife pulls him away. Right then, Security comes, and assumes the homeless guy started it, but check out his groceries in another aisle (they actually did a great job of diffusing the situation). The homeless guy wont stop yelling, and they are threatening to kick him out.
On my way out, i say to the manager, listen, that guy in the suit really did threaten that homeless guy. I heard him. He tells me not to worry, that the homeless guy is crazy (he doesnt speak english very well, the manager). As I'm walking out the door, the guy in the suit, starts telling the manager that he should make sure that "worthless F***" doesn't mess with anyone else.
I just wanted to grab this guy and scream, THE MAN IS HOMELESS. AND MENTALLY ILL. Where is your compassion? What pleasure did you get out of provoking him that way? Of course there might have been something I didnt see or hear since I was turned around, and I understand not wanting to be cut in front of, but why handle it THAT way? It made me very very sad. Is it normal for me to have felt this way?