There is speculation that he had an outstanding warrant, but no evidence that he did. In fact, the police report about his arrest makes no mention of any warrants.
True, if anything you would think that the police would be shouting about a warrant from the rooftops if there were one. But as another person said, with his arrest record there was a good chance he was on probation and anything from hanging out with the wrong people would have gotten him picked up. We won’t know the truth for some time though.