From what I can get, it's the design of the twitter feed. The article is attempting to show how deeply ingrained design and detail is in the company, along with being part of the team.
You'll often see internal tools will be the last place that design matters, because customers don't see it.
Yes, I'm not sure this is a positive thing about the company. I'm not buying design, I'm buying a service, and I am not sure design of an internal twitter feed would ever be something to blog about.
However, I am no designer, as it seems half of silicon valley is these days. Perhaps it matters more than I can see.
You'll often see internal tools will be the last place that design matters, because customers don't see it.