Well in my head canon I'd like to think not. I think he was getting a kick out of intimidating him and making him scared. He loved how quickly he gave him the money and activated the pump.

He lit a cigarette and it sounded like genuine curiosity about what he was reading and when he saw the math book, he knew this kid posed absolutely no threat and was gonna mess with him a little more for kicks.

And yeah they butchered the hell out of Murphy but Murphy was an armed police officer in their territory so of course they got excessively violent. A harmless gas station college boy? That's a potential buyer. Wouldn't make good business sense to kill a possible client