I have read it. But honestly, I don't think what it says is true. How is the ADF supposed to turn the tide if it was not designed to do so ? It's hard to imagine without user interaction.
The manual also says that you have to turn the sheet manually if you want to copy on both sides.

i bought this. YES it can do double sided but only via a manual feed glass. with auto feed no

I bought it too. Double-sided copying only with manual rotation on the scanner glass. There is a clear instruction on the display. Double-sided printing of course no problem