Do tell, which are a couple of those ways that someone might accidentally pick someone else's lunch box, open it, and start eating some unknown food without realizing?
And that’s not a hypothetical. He hasn’t confused our lunches but we do use the same style Pyrex containers. Mine is usually in a bag with fruit and such, but occasionally I put it in the fridge by itself.
It would be easy for someone to think some food was leftover from the day before, or that an apple or yogurt was meant for anyone.
You come back to a missing lunch and become incensed, but start to cool off when given an explanation.
Oh! and another: We have a certain corner table in our lunch room where we traditionally put free food. Someone set their lunch item there while doing something else. I grabbed it and ate it. When we realized I apologized profusely(while other co-workers said "oops, she shouldn't have put it there"), then bought her a replacement.
Also, especially in tech workplaces, never underestimate absentmindedness.