Alright so there are two explanations here and while a third might cause confusion, allow me to explain it. I was with GamerGate from the start and can remember most of the crazy shit that happened in the early days.
So, about a year ago a man by the name of Eron Gjoni stepped forward with a blog post. In the blog post he described how he was mentally abused in a relationship with a woman known as "Zoe Quinn", providing screenshots of chatlogs as evidence. He mentioned, in addition to threatening suicide to get what she wanted, cutting him off from his friends, and mistreating him on multiple occasions, that she cheated on him several times with 5 different guys.
One of the things people who read the blogs noted, was that several of the guys were her professional peers, including at one point her (married) boss and a game reviewer by the name of Nathan Grayson.
People start talking about it, only quietly at first, with one or two folks saying "Isn't it unethical to sleep with a journalist who might have covered their game?" Some even tried to go to game journo sites like Kotaku or Polygon to ask what was happening...
...what they got, instead, was mass bans on the topic. I'm not talking about just one or two sites here and there, I mean mass bans. A massively upvoted post on /r/games was wiped completely clean, the topic was banned on Polygon, Kotaku, IGN, even fucking 4chan.
When something is banned on 4chan you know something is up.
Eventually the only forum that would allow it was The Escapist forums, so people migrated there. They started digging and asking what was going on. Eventually the Journalists did responded... with 11 articles almost completely identical to each other and saying the same thing: "Gamers are dead". They called gamers "wailing hyper-consumers", they insulted them, derided them, then told them their identity was dead and gone.
Now this came off of several OTHER controversies of varying seriousness, all of which involved the gaming press stating that Gamers were "entitled spoiled children" and essentially saying Gamers were horrible.
That was the straw that broke the fucking camels back. Gamers accused Journos of being part of some clique, of colluding to push the same message and protect Nathan Grayson and Zoe Quinn because they were part of the clique too. The Journos responded by saying those were all lies and fantasies, that Gamers were just making it up, and that the only reason the articles might have seemed similar is because the majority of people can agree that Gamers are terrible human beings.
Well in comes Breitbart, Milo did a bit of digging along with some other anons digging things independently; they came across a list called "GameJournoPros", where people that were alleged competitors would talk and get together. In the list people saw that they DID agree to collude, not only that, but they began threatening members who refused to shut down any conversation on GamerGate in their forums, trying to guilt trip them or angrily denounce them, they'd do anything possible to make sure this topic died.
That's when Adam Baldwin coined the hashtag #GamerGate on Twitter. After years of the press propping up ideologues saying the hobby promoted some kind of "eeeeeeevil hatred of other races/genders", after what felt like YEARS of the press saying Gamers had no right to complain about anything, whether it was DLC or piss-poor reboots, after every insult they could muster was thrown at them, Gamers finally had fucking enough, this was a line they drew in the sand and they vowed not to budge.
So far, they hadn't.