All social platforms are advertising publishers. Facebook is an advertising company (though they refuse to say so; calling themself a publisher is a legal liability for them), they make almost all of their revenue from selling ads. YouTube is an advertising company as well.
Working with technology (and even developing your own technology) doesn't make you a technology company. insurance companies employ software engineers, but they're still insurance companies.
Even if twitch fails to make any money at advertising, they're still an Advertising company.