The last time I looked at Angular Material was quite some time ago, but at the time I was really surprised because it didn't follow the conventions established in the docs, and the conventions it did use seemed nonsensical given the design of the Angular framework.

I can only guess that "same team" was a design-centric subteam for Angular while the engineering-centric team worked on the framework/documentation itself, or that Angular Material was under pressure to get implemented before all the best practices were established and by then they were stuck with the API.