Simple: If It Fits Your Macros. This basically means that if your goal is up to 50 carbs in a day, and you currently have 20, you can eat 30 of anything you want without leaving ketosis. Harder: There are a lot of people out there who have a lot of weird interpretations on what Keto is, from misrepresented science to borderline religion. Some sites/groups are strict about what foods "are Keto", this often has to do with a breakdown of carbs as a percentage. This is not based on science though. Your body produces ketones when glucose is significantly restricted, that's it. It doesn't know or care whether that came from tuna or Krispy Kreme. There are lots of lists of "Ketogenic Foods" so some of this may stem from that, but these lists are typically just very low carb foods. This is not a list of magical items that create ketogenic states better than others, it just gives people who need more variety a list of options.
Hopefully intelligent answers to common Keto questions.