Was this racist ? I don't get it!?

So I was riding my bicycle in town and I'm a brown guy due to being half Egyptian so anyway it was a red light so I pulled up and stopped next to a car with two frat boys, so one of them goes "good afternoon" so I say "yeah", he says "welcome to mcdonalds... can I take your order ?", so I said "you can **** off", anyway they shouted something and ****** off, but I have no idea what the base of that was, was it racist, or just a random insult.