Yes, a report have to be made for the police in Thailand to do something. We read about it over and over again, when foreigner get beaten by security guards for example. If the foreigner no make a case, they can´t do anything. It´s silly, but it seems to be the norm.
Absolutely, I also doubt they were clueless, but just didn´t care. I might also say that sometime since 2014, somebody must have made a report already, but you are right, laziness is a big habit in the force.