Why would a guy I know tell me that I am acting like his enemy when I did nothing to him?

Only one person can answer that unequivocally. Certes, the details provide little in the way of informative description.
As an example, this might stem from actions which you deem insignificant, or certain behaviour he expects from you, or there's some misinformation passing around in rumors of your antagonism, or it's just a joke.