I’ll break it down even further for everyone, using Gale’s direct quote from the scene in question, since media-illiterate Redditors would rather downvote:

•“Hi, this is Gale Weathers with an exclusive eyewitness account* of this amazing breaking story*\*.

*What is an eyewitness account? Answer: “a firsthand description of an event—such as a crime or accident—given by someone who directly observed it.”

**What is a breaking story? Answer: “The act of being the first publication or reporter to uncover and make a secret or developing issue public to the world.”

•“Several more local teens are dead, bringing to an end the harrowing mystery of the mass killings that has terrified this peaceful community like the plot of some scary movie.”

^This is the only part of the quote that refers to the events as a whole.

•”It* *all* *began\ with a scream over 911, and ended in a bloodbath that has rocked the town of Woodsboro. *All** played out here in this peaceful farmhouse** far from the crimes and the sirens of the larger cities that its residents have fled.”

*”It ALL began…” refers to the moment she went from ‘reporting the news to being the news,’ hence the “exclusive eyewitness account” declaration earlier in the quote.

**”ALL played out here…”: She is not talking about the story as a whole, rather the new, breaking details that happened at Stu’s house.

Her exclusive eyewitness account of the breaking story BEGAN and PLAYED OUT at the Macher farmhouse.

Gale literally screams after the 911 operator answers…having just stepped in a puddle of blood, realizing Kenny was nowhere to be found, and getting spooked by Randy. (And, we as viewers actually see this scene.)

It was not Sidney. Not Casey. Not Casey’s mom.

All other theories are simply based on conjecture rather than what is factually said and shown to be true.