"Download", as used in practice on the internet when referring to documents generally means copying the whole thing to your computer such that it can be used there without further internet access.

It generally does not include temporary transfer of small parts of the document for immediate reading, except when the focus of the discussion is about the underlying mechanics of the transfer.

This supposed duality is nonsense. A change of cache settings in your browser amounts to the same result. There's no such thing as a "temporary transfer", and I think we should not entertain the notion.

I don't see how it's any different from time-shifting with VHS. In this case, you're just using a longer-term "temporary" format (epub, mobi, pdf) which allows you to peruse the website later.