Could you explain that please?
In "The Origin" Buffy is in the library with Xander and Willow around season 2 telling them about her life in LA and how she first found out she was a Slayer and discovered the existence of Vampires.
The story is a retelling of the film, but the comic itself was written during season 2 or 3's airing so it only matches the continuity of the first three seasons.
At no point during the comic does Buffy tell her parents she saw Vampires and all they knew (in fitting with season 1) was that she burnt down the gym and was a trouble maker.
In season 6, a few years after the comic was written Buffy tells Willow that after she saw her first Vampire she freaked out entirely, told her parents, and they put her in a mental institution for several weeks, after she got out they moved to Sunnydale and enrolled her there.
The episode implies that she saw them, was so scared she started the fire that burnt down the gym and was institutionalised.
But it ignores the events of The Origin entirely, and since its whats on screen that counts as canon, the film plot was essentially "re-erased".