Just working from memory, I’m pretty sure that the term “Hispanic” was a concoction of the Nixon administration.
Nixon and Senator Montoya from New Mexico were part of it. Nixon saw Hispanics as a counterweight to the black vote and Montoya, a Democrat, coined the word “Hispanic.” The label Hispanic was chosen in part because in New Mexico people of Spanish descent such as Montoya referred to themselves as Hispanos, which was anglicized to “Hispanic.