When I say myth, I mean in the sense that it’s not actually supported by the Tripitaka, which is the first complete written account of Buddha’s teachings by a lineage of his original monastic order (mostly confirmed by historical evidence where it exists) to survive as written to the present day, and considered canonical Buddhist teaching.
It is most definitely quantifiable whether something is or is not written in the Tripitaka. That is why it remains important and historically significant.