According to an article you found online. That's exactly my point, if we can't trust news sources then we can't really know anything. Because of my aforementioned distrust of Fox News, if it were written by them I'd dismiss that article out of hand placing no truth value on it either way. I'd expect somebody that distrusts CNN to do the same if it were written by them.
"It's confirmed!", "They admitted it!", and other unprovable internet turns of phrase in comments sections are really just "I believe it because somebody I trust said so" and that only has weight as long as trust has weight.
If the accused admit to something it's more believable than the alternative (that they were forced into false admission).
So in this case if the Ukrainian government admit to making things up then I would think it's believable that they made something up for the sake of propaganda. We can also check more independent sources --read Japanese news, or Indian news sources, etc.
We don't know that the accused admitted to anything. We know that the Washington Post says that they did. The world becomes very solipsistic when you lose trust in reporting.
