Got screamed at for doing nothing

I'm a long distance runner and today I halfway through a planned 15 mile run when I stopped at a convenience store to get buy some Gatorade and take a break. I don't bring my wallet with me on runs, just my phone and use Apple Pay. I bought my gatorades and sat down at a picnic table on the property to cool off when a homeless looking guy came over with his drink and food and sat at the table on the other side. No biggie, I thought, I'll just mind my business and let him mind his while I'm practically gasping for air just trying to cool off.

30 seconds later a guy pulls up in his pickup truck in front of us and gets out and points to the homeless guy and asks "you motherfuckers want anything?" and the homeless guy replied "if you're paying then sure" and the truck driver replies he'll get him something. As in finishing my drink he comes back and gives him a few Red Bulls and then asks if I want anything and I said no, I'm just here on a run and then this guy flips a switch and just goes ballistic on me.

"Oh you're not with him? You're seriously lacking social awareness" I was taken aback and just asked what he meant by that and he goes on a tirade about how I'm an asshole and should've just given him $20. He ignored me when I explained I don't have cash or my wallet on me and am just trying to sit and have my Gatorade when he gets back into his truck. I thought the conversation was over when he rolls down the window and continues screaming at me as he's leaving and driving across the parking lot about how "you're smart stupid, you're everything wrong with society and you're a motherfucking terrible person". I just replied to tell him to have a good day since I didn't have the energy for an argument and he told the homeless guy to have a good day and for me to go fuck myself. This whole time the homeless guy was just watching not saying anything.

The guy did a good thing giving a drink to the homeless guy, but I'm really not sure why I had to be the villain in his story. I'm really not sure what set this guy off, if it was drugs or alcohol or if he just was having a bad day. This guy doesn't know anything about me except that I was sitting at a table drinking Gatorade when he assumed everything about my life story. Just a bizarre situation all around. Makes me worried for the people in his life that have more "reason" for him to yell than a random guy just sitting with a drink.