This is yet another approach to the age-old problem of food thieves around the office. Reproaching a coworker is challenging business; you need to be aggressive enough to get the message across loud and clear, but at the same time, you don’t want to get into ugly confrontations, as you want to stay on good terms with the people who work with you.
For this person, it seemed like the obvious solution to deal with his food thief was to get revenge – feed him cat food. While this taco probably tasted weird to the person eating it, it’s possible he didn’t even know he was eating cat food. However, the person who devised this plan would still feel victorious, as he’ll always know the thief was served what he deserves.