Does look like a cut. Any chance they could have licked the edge of an open tin or its lid? I always have to put tins straight in the recycling otherwise mine will be all over them, even baked beans and tomato soup, absolutely anything! Like PP said keep an eye and if not healed in a week or starts showing signs of pain or infection then definitely vets. Cats are notoriously good at hiding pain though, so like someone else said, watch for dropping food when eating or not eating as a sign of pain. Chances are it will be fine though!