The source is in the article, actually. This is the order from FSB that MTS operator received. They translated this as: “the mass distribution of obviously false reports of a terrorist act” in January, resulting in “mass evacuations of schools, administrative buildings and shopping centers.”

Right before the IP addresses list, you can find terms "blackhole", "BGP".

The document has a signature of a head of the FSB center that handles this types of requests and orders. Also, you can see a stamp in the right bottom corner on the first page.

Full story, how a Russian internet company has actually found out about blackholing can be found here (in Russian): https://habr.com/ru/company/tm/blog/443222/ In the story, you can find that MTS confirmed that they are blocking traffic and referenced the order in the original article.