Did other providers have similar issues to Cloudflare? I only noticed cloudflare sites being particularly down, not other CDNs, but maybe that was selection bias?
Only the main twitch site seems to be using fastly, the streams are powered by AWS' infrastructure as far as I can tell, which would be expected, seeing as how Amazon owns Twitch.
ISPs often have Youtube and Akamai caches forward deployed to their networks, which would reduce the dependancy on big ISPs. Google also buys a lot of its own international links so it can pair directly with or close to ISPs, so big ISP issues don't affect their services as much.