An internationally circulated news outlet could not possibly do this in error. They had plenty of time to think about what they were doing before the story went to print. Every reporter and every editor learns early on in their careers as journalists not to print anything that constitutes libel or slander. The Guardian has proven consistently that they throw caution to the wind and rely on sensationalism rather than facts to sell copy.
Sunni Arab nations are 'Israel's allies,' says Israeli Foreign Ministry director general (JTA)
from the article: Guardian: Our Israeli organ harvesting headline was serious error