Is Apple's Vision framework use Zxing under the hood?

What's the difference? You can only use the public API. If you tried to access any lower-level methods, that could be considered a private API and be grounds for rejection, or worse. Apple might swap out the underlying API for their own implementation in some minor OS update. Your app would break if you used the Zxing API.

PS: You should probably edit your post and remove that URL. Apple only recently allowed people to post non-Apple URLs in this forum. Apple might not appreciate the "adult" content of that URL.