So let's try to be clear: this saying does not mean "stay ignorant, don't respect knowledge others have accumulated and formalised for your benefit, please re-invent the wheel!"
What does it mean? "If you think you understood what buddhahood is, start again! Who are you, really, beyond the conventional labels of a name, a CV, etc.?"
It means "Kill the concept, the preconceptions, the prejudices, the ideas you have about what it means to be a buddha. The Buddha doesn't wear a badge stating he's a buddha; so, if you meet the Buddha on the road, you are making him up, in your head!"
It means "Don't cling to a myth, don't cling to a nice story (regardless of how historical it is, or not), don't cling to what you know, don't cling to ideas you make. Keep looking!"