I believe the hiring is a facade. They have been sending out hackerrank tests to every new grad but never planning to follow up. As a matter of fact, they stated that they will "follow up" in December. Any serious company in the Bay Area wouldn't be this slow with hiring if they were not in trouble.
I don't disagree with your conclusion about Twitter specifically, but it always blows my mind how slow tech companies are to deal with candidates in a hot job market.