One can encounter overzealous gate agents anywhere in the world, with food and other items. Many of us have had experiences. If you have time, ask for for a supervisor to clarify the ruling by the check in agent. You have that right, but many passengers do not bother, or are in a hurry to board. I think the best tactic is to allow yourself ample time to clear security if you have unusual items in your baggage, carry on or checked. This allows enough time to have your baggage items examined. I've brought compliant food items into the US in my checked luggage without issue. If in doubt, ask.