After watching the video myself, I found a few takeaways relevant...

1. He is denouncing forms of crowdthink.
2. He denounces the way people on Lemmy tend to grab sources and distribute biased knowledge.
3. Key red flags he gives describe the core fabric of Lemmy's culture, such as when he says it's a red flag when we interpret peoples' intent for each other or try to tell each other how to feel about certain things.
4. The very beginning of the video has him talk about the difficulty of defining a good source over a bad one due to how we cannot be certain of anything and how our ideology might be natural to us only due to our circumstances. People on Lemmy tend to not think in any terms other than "if it's what I'm accustomed to, it's right".
5. He talks about sources in a way that makes all the instances of people on Lemmy complaining about others sealioning look bad.
6. OP is historical on Lemmy and has seen all the things he talks about converge on her in ways that violate absolutely everything he says (one of the key ones even has a community trying to establish sealioning as inherently wrong). It's buried now, but look up material related to "Leni, "Lenny", or "Call me Lenny/Leni" (that was their full screen name). This individual who led a witch hunt against Leni (short for Madeline, if you get tired of saying Leni) even got the whole fediverse to violate the "indicting a whole demographic" red flag because this place is far from his way of thinking, not that it isn't common for them to do this to big businesses in general. I remember getting mixed into it just because I merely asked about her and shared a meme and being accused of being Leni.

I am currently running an experiment about this as an example in progress.

What doesn't it apply to?