What caused it are the journalists that moved their work from on the ground reporting to on the twittersphere reporting. Rather than go out and see what people feel, they decided they could just sit at home and browse twitter as a stand-in replacement for public sentiment.
This gave an enormously disproportionate voice to the fringe groups that had long been deeply entrenched in the online space.
It may appear so, because that’s how the actors involved use social media, but it’s not caused by it.