Take this post for example: https://www.reddit.com/r/northernireland/comments/1ll6ocg/see_it_say_it_censored_kneecap_is_not_the_story/
Speaking from experience, people in Ireland are overwhelmingly pro-palestine.
There is this user in the comments: https://www.reddit.com/user/EntireCourage308/
Its a nearly year-old account, it started posting about a month ago, it made some innoculous posts, then pivoted to posting far-right misinformation in the r/northernireland subreddit.
There’s loads of other accounts just like it.
Even with it being federated I don’t see how Lemmy could be immune to astroturfing. I’m sure there’s some already going on. Lemmy just isn’t yet popular enough to be a major target. Instances can defederate from one another but it’s trivial to create a new account on a different instance and resume turfing. I suppose the openness of Lemmy’s logs, when compared to the closed-source centralized nature of reddit, could help suss out turfers though.