Well, infamous fanfiction is basically fan - made stories that are known for being bad in some way. It could be that they break the unwritten rules of the fandom. Maybe they rewrite the characters in a completely wrong way, like making a heroic character into a villain for no good reason. It can also be due to the author's behavior. For instance, if an author is known for plagiarizing other fanfictions or being rude to readers, their works can become infamous.
I think it's more of a fictional creation. While some stories draw inspiration from real life, this one might have just taken a few concepts and built a fictional plot around them in 2020.
Most probably not. Usually, works labeled as 'Infamous' are fictional, crafted by the imagination of the creators rather than being rooted in real events.
In my opinion, whether the St Augustine Fort ghost stories are real or not depends on what you believe. Some might dismiss them as just old tales, while others who have had personal encounters that they can't explain might be more inclined to think they're real. There could be natural explanations for some of the reported phenomena, like drafts of air being mistaken for a ghostly presence, but the allure of the stories remains.
Since we don't know the exact context of 'the infamous man', it could be anything from a superhero - related fanfic where the 'infamous man' is a super - villain with a complex past, to a historical - fiction - based one where he is a real - life figure with some fictionalized elements added to create an engaging story.