“Straightforward harrassment if true..”
Not quite correct. If the police have arrested him for harassment they may struggle to sustain the charge. Case law dictates that to sustain a charge of harassment the accused must have engaged in a course of conduct causing alarm, distress or intimidation to the victim. The “course of conduct” must amount to at least two separate episodes. So you can alarm, distress or intimidate somebody once and it is not harassment. Do it again and it is (provided it can be shown that the two episodes were conducted with a similar aim and/or for a similar reason).
However, having explained that, I honestly don’t see quite what the police are going to charge him with (if anything at all) and a decent brief would now be making plans to take action for wrongful arrest. All the man has done is to post a message saying that he conducted a (somewhat one-sided) conversation with a woman. Posting the message is not a crime. Neither come to that is the conversation - if it took place at all. There is no confirmation that it did, presumably no complaint has been received from any alleged victim or anybody else who may have felt intimidated or alarmed by it. All the “Tweeter” has to do is to say his story was made up (which, by the sounds of it, it probably was).
The police need to shape up. There are plenty of things they could busy themselves with without wasting time on mindless numps.