In your Kindle App on your Android device, at the top of your Library tab, there are options for ALL and DOWNLOADED. If you are looking at the "ALL" list, it's showing you what's available in your Amazon account and giving you the option to download it from there. This is not related to Calibre in any way.
To delete books from your Amazon account, go to
https://www.amazon.com/hz/mycd/myx and delete from there. If you do that, you're discarding a book that you purchased, and you'll have to buy it again if you ever lose the copy that you had downloaded and imported into Calibre. For most people it's better not to delete purchases.