Although the heat-sensitivity of Krokorok eyes is typically described today as night vision, it is thought to have initially evolved as a way to seek out fire pokemon, against whom they have an advantage. Although they are capable of distinguishing forest fires from pokemon, primarily because of the former's immense size, Krookodile can not say the same about fires lit by humans.
Since humans first tamed fire for cooking, Krokorok has appeared in human lore as a remarkably foolish villain. For although Krokorok are known for smashing into houses and campsites in search of food, they are poor at recognizing the nature of their "prey", and initially mistake the fires for some undiscovered species of fire pokemon. Only after a few painful bites of nothing but fire and air do the Krokorok realize the deception, but a burning, angry Krokorok will not turn away with an empty stomach.
It is then that the scene becomes a battle – for Krokorok are not entirely wrong for associating human fires with food. Some steal the many morsels which were being cooked for human consumption; others, treating the humans who stoke the fire as the responsible fire-type, attempt to devour them. The surprised humans will inevitably fight the Krokorok off, for these pokemon have already been significantly injured by trying to eat their fires. A few will use fists or iron tools, but the most common weapon against the Krokorok is the nearby flames themselves. Should the Krokorok be defeated in the fighting and fail to escape, humans will gladly take the opportunity to replace their stolen meals.
Humans are typically considered normal type, and a few consider them fighting. The Krokorok consider them the most dangerous fire type, and considering their perspective it is difficult to say they are wrong.