I think this is just applying the same informal writing style used in, for example, online chats with friends, to a relatively-informal blog post. I don't think this has anything to do with the Bay Area or its tech industry in particular.

Wow, I read the whole thing without noticing that.

But as someone who came of age in the AIM / ICQ / IRC days, it feels pretty normal. That's just how we wrote. I still fall into it by accident when the context is right and I'm not thinking about it (eg Slack at work). I hope youngsters aren't judging me for it.

I believe you can thank Verso for that:

https://github.com/leanprover/verso