Yudkowsky is well-known for his work in AI. He occasionally makes jokes, but it’s usually about AI (not relationships). I know that on his profile, it says something like “when I don’t use punctuation, it’s a joke,” akin to Reddit’s /s.
And yeah, he left off a period on the first post, though not the other two. But that said, he rarely makes multi-part jokes. It’s pretty clear to me, having read his posts and articles for a while, that he means this.
To further clarify that this is a “rationalist” of the highest order, consider that he wrote a half-a-million-plus word fanfic of Harry Potter, but with Harry studying science instead of magic: en.wikipedia.org/…/Harry_Potter_and_the_Methods_o…