Well, it's not a straightforward yes or no. Usually, it depends on various factors like how closely it adheres to the main storyline and if it's been endorsed as canon by the production team.
Anime canon refers to the content that is considered official and part of the anime's storyline. Manga canon is the content that is officially part of the manga's story. Usually, anime canon is based on manga canon but can have some adaptations or additions.
Definitely not a true story. FNAF is a work of fiction that takes place in a fictional world with its own set of rules and scenarios. It's all about creating a thrilling and immersive gaming and storytelling experience, not reflecting reality.