Yeah, the reports are obviously fiction. I don't know how one pursues this line of thinking (as you say), other than to evaluate each report and give it critical analysis. A kind of forensic inquiry.
The BF sighting reports have always reminded me of the published "letters" to Penthouse Magazine. I snuck my dad's copies as a kid, and read them when he wasn't around. The letters are meant to create sexual fantasy in the mind of the reader by taking them right to a supposed fantastic sexual encounter that happened to the writer. Some may actually be true, but it makes no difference either way. They typically sound like this: "My boss at work is a gorgeous middle-aged blond with an amazing figure. I've thought about screwing her many times, but never pursued it and we have always had a good professional relationship. But last Tuesday changed everything. Stacy came into my office at about 3pm, giving me a look that she has never gave me before. A button was undone on her blouse that had never before been outside of the confines of the hole designed for it. My mind was spinning with confusion, but my instant hard-on told me the ultimate truth about what was going on and how the coming evening might play out. She parted her sultry lips to say...."