whether or not you get your news from a site is distinct from whether or not that's the reason it exists. It would be a pretty tenuous stretch to say Reddit is a site that exists to give people news, even if many people do get their news there.

The same applies to Twitter. It does not in any way exist to be a source of news, but many people do get their news from there, for better or worse.

But they're both just social media sites. Anyone anywhere can post whatever they want and mostly get away with it on them. There is no vetting except in certain extreme circumstances.