Well...yes. Just because something looks good, on the surface doesn't mean it's remotely compliant with the standards and devices that B&N (etc.) need for their customers. I mean...for example, I have would-be customers that come to me ALL the time, with faux-Word files that they made by opening a PDF and using "save as Word." When they see the result, OH HAPPY DAY!, it looks fantastic, right? Like exactly what they want.

But underneath, it's steaming pile of crap. MAYBE it can be used, again, exporting to PDF to make a new paperback, but if you want to use that cursed thing for an eBook, you'll get junk. GIGO. Without getting into the actual guts, you don't know what you do, or don't, have. I suspect that the HTML that your "buddy" made was like that faux-Word file; just garbage below the surface. Or hell, not garbage, but not clean enough to pass muster.

I don't know how your buddy made that file, so I don't want to disrespect his work. Might be fine for some other purpose. But if it was made by converting ANYTHING that was done for Kindle, based on your descriptions, using Calibre, it was a big waste of time. That dog, as they say in the south, won't hunt.

Hitch
That reminds me of this kind of thing: https://www.youtube.com/watch?v=SKfpYVK_r0E