It’s slang when used in this context and used a lot in my country(Australia.) But ultimately has a very similar meaning to the actual definition. Best way to describe it would be a combination of “appealing, sneaky and indulging” all combined into one. It’s kind of hard to explain but I can give you some examples to help you understand a bit. Going down to the pub for a cheeky beer after work. Doing a cheeky little burnout in my car. Again it’s an example of when a word is misused but eventually takes on its own meaning. Kind of confusing but hope that gave you some sort of understanding 😊