Zotero would import the feeds in the file — it obviously couldn't import other feeds not in the file, since the data has to come from somewhere.

To fix, you can either delete them manually or run this in Tools → Developer → Run JavaScript to delete all feeds:

var feeds = Zotero.Feeds.getAll();
for (let feed of feeds) {
await feed.eraseTx({ deleteItems: true });
}

Did you try to run it multiple times?

Are the feeds gone if you restart Zotero?