That is. It’s been blaring from their media for a solid year now, and is the stated casus belli of their invasion. It is 100% Russian-produced misinformation, leveraging the fact that people don’t know anything about Ukrainian history to attack them with false stories.
It’s an old trick. The Nazis tried to convince the world Poles were stupid and needed to be ruled by overlords, by misrepresenting and twisting stories with their propaganda. Poles never actually charged tanks with their cavalry, there are no records of that ever happening, from Nazi or Polish sources.