Thinking with simple common sense in this, they probably want you to have an understanding of general cleanliness and whether you have worked in an environment where cleanliness is important.
A basic knowledge of how easily viruses and bacterial illnesses can be transmitted through poor hygiene, such as not washing hands after using the toilet, would probably be useful. Think about all the places you’d touch on a train with your hands or bare skin in general, or where you may place food, and therefore surfaces that would need particular attention to cleanliness, especially in a public space.