Sounds like KLM were just playing it safe and that is to be commended. I was a pax on a flight a few weeks ago when a pax with a nut allergy was on board. The cabin crew did a PA to ask fellow pax to not consume anything containing nuts during the flight. However the company could potentially get themselves into a sticky situation since if someone does not understand the announcement due to language barriers then cracks open a good old packet of KP's finest - the airline will be held over a barrel!