There are many possibilities with this. The police might be covering something about the encounter up in order to hide how bad things really are in RIo. Or there is the possibility that the police really don't know what is going on. One way or another someone is not telling the full truth.
Yes, there are some people telling the truth. If Rio Police reportedly exaggerated encounters with swimmers, there must be some people telling the truth. Although Ryan Lochte did lie about getting mugged, as they were actually performing vandalism, there was some truth to the encounter. The Olympic swimmers were held at gunpoint.
Ryan Lochte admitted that he exaggerated the situation, though in reality it's just called lying. The Rio police did the same thing, to the point that it is impossible to tell who is telling the truth. Lochte and the other swimmers are a disgrace, as are the Rio police. Two disgraces mean you can't tell the truth.
The Rio police are bound to exaggerate the incident to make the swimmer's behavior look worse so they can justify their response. The swimmers clearly lied and admitted they had done so but we cannot be sure that their new version of the event is what actually happened on that night.