I think it would be more accurate to say that Bluesky is like pre-Musk Twitter because the moderation teams at both Bluesky and Original Twitter are primarily trying to remove/suppress posts that they consider to be illegal, violent, overt harassment, etc.; they weren't politically motivated. I am sure some conservatives will read this and be like BUT BUT BUT BUT -- but sorry, there have been a lot of studies done on this topic over the last fifteen years and change, and they've consistently found that conservative posts tend to outperform liberal posts on most social media, including Facebook and Twitter, and that the anecdotes suggesting the opposite tend to focus on posts that were moderated for being violent and/or overt harassment. Conservatives don't want to hear that "their side" gets moderated more often because they have proportionately more assholes that invite moderation, but as well-known Person In Need Of Moderation Ben Shapiro so aptly put it, facts don't care about your feelings.

So why did Bluesky end up proportionately more leftist (which is absolutely true)? Because while the moderation team at X may still remove/suppress posts that are illegal, X has, at a corporate level, very explicitly chosen a political side in a way that no other major social media company has. Bluesky's CEO has not, to the best of my knowledge, been promoting liberal conspiracy theories, hyping posts attacking conservatives, or joining the government to radically reshape it in ways that anyone even moderately right-of-center would find horrifying. When I read HN, it seems like those who still love Twitter/X seriously downplay how much of an effect Elon Musk's transformation into a loud, forceful reactionary -- and his insistence on making sure that Twitter/X reflects that transformation in the posts that it actively promotes to its users -- has had on its audience composition. Yes, I know there are still lots of people on Twitter who aren't Musk fans, aren't particularly political, might even be left-of-center, but his behavior has actively driven a lot of people off it.

tl;dr: Bluesky didn't actively choose to become left-of-center; Twitter actively chose to become far right, and those who were bothered by that but still wanted to be on social media largely ended up on Bluesky.