There’s no such thing as a “true story” in the completely literal sense. All stories are told from a particular perspective, giving the circumstances as they are or were experienced by particular people. Furthermore, this story was self-evidently not an attempt to impart literal fact, because names and locations and life histories and social networks were all transparently altered (and, indeed, completely invented). So it comes down to what the audience can be expected to infer from “true story”. Personally, I inferred that it provided an emotionally real description of how a particular real incident of stalking was experienced by a particular real individual, but I did not infer that Martha was truly a lawyer, truly went to jail, truly walked after him down that specific canal or truly heckled him during the final of that specific comedy competition.