A logical answer is that Puzo was trying to get a free ride on history, just like lots of other authors do. He knew something of NYC Mafia history, and so tossed in a chapter from the famous Castellemmarese War of 1930-31, but confused Salvatore Maranzano (the victor, and thus the guy that Vito was most like in the scene you cited) with Joe the Boss Masseria, who lost, and who was gunned down in a restaurant with "his mouth full of bread." Later in the book, Puzo portrays Vito as attempting to reason with another Don who was notoriously hot-headed and homicidal. Finally Vito gives up and says, "But no one can reason with him." That Don is later assassinated in a barber shop. In other words, he's Albert Anastasia, and Vito in this case is Vito Genovese. Vito is called the biggest olive oil producer in America, therefore he's Joe Profaci. He arranges for the assassination of Moe Green (who's Bugsy Siegel), therefore Vito is Lucky Luciano. And he retires after being shot by a rival, therefore he's Frank Costello. And on and on...