As far as I can see there's only 2 strategically logical reasons to admit to something like this:
You know for a fact you can't pull it off anymore/the Russians know this happened so it's not new information and so spilling the beans is a means of humiliating Russia and winning some good PR.
It's not actually true and you're just fucking with Russia and making them second guess things (and also humiliating them if people believe it).
Beyond that it seems really careless to give away some juicy info like this. Just because they might not have a counter to it now does not mean they couldn't develop one now that they know it's a factor.