In America, when children grow up, parents could have that talk with them about how George Washington really was a great guy and how much they appreciate if their children wouldn't cut down the cherry tree in the garden but also about how this story about George Washington is just that - a story.
I wasn't there at the time, so this is just my take on it: I imagine in the USSR it could have been dangerous to talk to children like that and one way out was to exaggerate the stories until the child notices what's going on. Now daddy Sergei Kurekhin was doing that to the whole Soviet Union - and that's why they laughed about it.
[1] I call it a joke and not a hoax, because I think hoax kind of misses the point. I wasn't there at the time but this is my opinion: I don't think anyone believed it, I think people didn't say so partly because they didn't want to destroy the joke and partly because this was still the USSR.