Most people would be upset to see their lunch being eaten by someone else, especially if it is coworkers, as it shows a lack of trust and respect.
Consider the statement "I was upset and puzzled to see my coworkers eating my lunch I had left in the company refrigerator.". Is the statement "I was not at all upset to see my coworkers eating my lunch that I had left in the company refrigerator." false? Yes/no/unknown