I've also been thinking a lot about the person who found the dog.
Am I right in saying that they came across the dog with no harness on, then put the harness back on the dog and tied it up? I find it strange that anybody would do that and not take the dog/phone with them?
They then raised the alarm sometime later so the dog was left tied to a bench and the phone was left too and nobody else encountered any of that until presumably (the partner?) was alerted and came down to rescue the dog who had been tied up for over an hour? No wonder the poor thing was agitated.
The whole situation is really bizarre, surely most people would survey the scene if they came across a loose dog and discarded phone, did they check the river? Why were they down there if they were rushing off to an appointment?