I found it surprising because I interacted with their REST APIs first. They are very good about docs. The ones I use most frequently (TS) are no exception, though they have some gaps. But the actual REST APIs I integrated very clearly predate a lot of their guidelines or struggle to follow them.
Comments were very insightful as always. I kind of agree with OP, this article is very thin on content and mostly peripheral take on good API design. It is unhelpful.