Yes, Kyshtym was a radiological catastrophe at Mayak in the Soviet Union. It is considered the third most serious nuclear disaster to date. Numerous villages were subject to the radiation after the explosion, but only several were immediately evacuated, leading to devastating health effects in the immediate population, as well as future generations. Birth defects and severe mutations riddled that area's population for generations. Without knowledge of the Kyshtym disaster, the Russian population will be unable to prevent similar disasters.
Kyshtym disaster was more than 50 years ago and now the level of radiation in Ozyorsk itself is claimed to be safe for humans. But to keep honest and open relationships with society, government should release this information. So it was right decision to show that area is still heavily contaminated with radioactivity.
We don't know exactly what happened, or what information was released in Russia, and their government has the same right to figure out exactly what occurred before releasing details as the United States government does. Our own government often withholds the details of disasters until they can complete a full investigation and initiate a response.
Many governments make poor decisions about what they should do, didn't do or could have done. Their choice to keep the disaster a secret may have been motivated for political reasons, but it was their choice. They have to take responsibility for that choice, be it in 1957 or 2015.