Among the contemporary sources is Sir Sidney Smith, who is the original source for the story. It is Sir Sidney Smith who lied about seeing Napoleon leading the executioners at Toulon. Is his testimony more reliable that the inhabitants of Jaffa, who never heard of the story? Why is the Jaffa story so well-known (as it should be) and the Uva-Wellassa Massacre story not?
Do I personally think there were executions? Yes, probably. Were the numbers as large as bandied about? Maybe not.