I'd find it hard to believe all the cities in Spain decided to expel the Jewish people all on the same day. The inquisition began decades earlier so there probably were indications something bad was going to happen
They're probably referring to the Alhambra Decree [0], which did expel all Jews by a set date. That date was the end of July, and Columbus sailed on 3 August, so it's very close but not quite the same date.
