Yes, calm down everyone. "He was released without charge", is sloppy journalism. The police spokesperson said that enquiries were continuing, and at the same time appealed for witnesses.
The seller was arrested on suspicion of theft. There is a rebuttable assumption in British Law that a person in possession of recently stolen property is the thief or a handler. He will have been interviewed about his possession of the bike. I cannot make any assumptions about whether he answered questions, or whether he gave an explanation, but the most likely scenario is that he has been released on police bail to return to the police station at a later date, while the police seek further evidence, which may or may not involve seeking evidence to refute or confirm an explanation that the person gave.
Even if he was released without charge, which is a practice sometimes employed by the police, he will have been told that further enquiries will continue, and if further evidence comes to light he is liable to further arrest.
So, pitchforks back in the cupboard please.