That one happened because Gemini read it on Reddit and hadn't figured it was a joke. It was only up there from its launch through till about four days later when someone removed it.
They are getting better at fact checking, Google apprently working on Googling the answer - Hassabis at Davos the other day: https://youtu.be/ICv03VysLaE?t=826
It already exists in Gemini and it existed in Bard....now it's called "Double-check response". Here is pic of it in action: https://i.imgur.com/aIISzt5.png