That may have been what they said to the Western media. It does not necessarily match what they said to their own government run TV channels and newspapers.
What do you mean? The Soviet announcement is right there in the video. It's an announcement on Vremya, the official evening news TV program broadcast across the Soviet Union.
The accident happened on April 26th, and was acknowledged 36 hours after when they began to evacuate Pripyat, a town in the immediate vicinity of Chernobyl. As I said, it took about a day for them to acknowledge it, and it was only acknowledged when it became clear that it could not be swept under the rug. Your video does not contradict that.
You wrote "Initially there was a flat out denial that anything happened at all, but once the scale of the catastrophe became clear (within about a day)". That's not what happened, you can look it up in any of the numerous timelines and accounts of the accident and the reporting and Soviet disclosures. The evacuation of Pripyat started before the first public Soviet announcement as described here:
Maybe it's been edited since you supplied the wikipedia link, but it doesn't support your narrative.
One page down, it describes Ukrainian Soviet officials claiming there was no danger from the accident to regional Ukrainian SSR officials. It says that Pripyat was only evacuated 24 hours after the disaster, after more than 50 residents were hospitalized for radiation poisoning.
Even then, the letter to the residents was that the evacuation was temporary, and primarily as a precautionary measure.
The only thing you effectively refute is the timeline, Pripyat was evacuated 24, not 36 hours later, as the parent poster erroneously stated.
The wikipedia article doesn't mention internal Soviet press releases, so you haven't refuted that Ukrainian or Russian officials denied a disaster. However, the parent poster nor the OP haven't demonstrated that officials lied to the public either.
This isn't from April 26th 1986. How can it possibly be, the 'Western press' didn't know about the accident then. It's also not a 'flat out denial anything had happened at all', you're just misremembering that part.