In Spain (including Ibiza) English is widely taught in schools under the national ESO system. It is one of Three languages available for tuition to 14 and 15 year olds, the others being French and German, English being the language most commonly taken up by pupils with German a distant second choice and French way back in Third.
It is obvious that no-one inferred that English is spoken ahead of Spanish amongst Spanish nationals. But having been to Ibiza many times as well as Majorca, the Canaries and the Spanish mainland, I can assure visitors that English is indeed quite widely understood (if only in basics) amongst much of the population, particularly those who work in the tourism industries, cafes, bars and hotels, I have also had no problem with being understood by the majority of Taxi drivers on the island.
German is also well spoken and understood, but it is a fact that twice as many Britons as Germans visit the island every year.
As for being picky over a one mile difference in the length of the island....PLEASE!