I suspect that as with many off-shots they hate the original community.
https://www.cbsnews.com/news/vermont-border-agent-death-expo... is a better, longer form of this article
It seem they were a fan of Eliezer Yudkowsky and maybe Nick Bostrom (although a bit unclear) but they hate MIRI
LessWrong has a summary of their involvement: https://www.lesswrong.com/w/j-lasota-ziz
Calling themselves rationalists are more ironic than a concentration camp having a sign promising freedom to those who work.
She also recruited some of her cult members from the community (not sure which ones).
So, if you want, you can frame it as the rationalist community being a dangerous place that attracts sick people. Or you could frame is as anarchists being violent, vegans being intolerant, or trans women being crazy... because the Zizans are all of that. Everyone is free to chose their own story about them.
It may or may not be important that most rationalists / anarchists / vegans / trans women are not crazy murderers, so maybe the story is mostly about Ziz being Ziz and succeeding to get a few (less than ten) followers.