It is a myth. Alan Block, a professor, set out to do a story on it for his 1979 book, and found there was no evidence of it ever hapening. No one can even be sure if the two deaths in Jersey were related to Marranzno or Masieria, they are just the only two deaths that could be found that day. It is a fairy tale that grew into a legend, and though it was debunked, people still repeat the story as truth.
Good post. And the same can be said about a lot of other bullshit stories on the Mafia. For example (just off the top of my head) the claim that Capone was responsible for hundreds of gang killings, the claim that Luciano was the one who formed LCN etc, etc.