Not hard to believe - younger people make up the bulk of their audience, and probably the bulk of HN that trend more liberal. That's a reflection of the userbase though, not necessarily of Twitter or HN's views. I would bet most LPs are more conservative - if only in private.
It’s not a bad thing, the same way that Fox News being conservative isn’t a bad thing. It just is what it is.
These are major news sites. News always has a bias. It’s important to identify, for one’s own sake.
It’s not even particularly hard to bias an AI algorithm. It’s arguably the default.