Overreacted but stayed calm

So when I first got to work someone asked for a pack of backwoods. I denied him due to him not having his ID he got mad and said that I didn't ask him last week. Which was a lie but I told him that I just need it. He got mad then calmed down and said "stay safe and have a great night." With a dead stare and left. Then after a few hours he came in just a few minutes ago, I saw him walk in and I said "hi, how are you. " he then walked up to me put his hand in his coat then stopped and stared at me for a second then walked out. Scared the shit out of me. I told him to have a great day. I stayed cool but on the inside I was freaking out. I don't know if he was trying to scare me or changed his mind on what he wanted to do but I seriously need to get a different job especially after that shit.