There are two sentences in the the on-line version of the research paper worthy of note:
"The majority of women worldwide do not have orgasms during intercourse..."
and
"Female orgasm is possible in all women...during vaginal/anal intercourse simply by stimulating the clitoris with a finger."
I point out that this is a retrospective paper. That is, no original research was performed; rather conclusions were drawn based on information found in prior publications. In such a paper, one can support pretty much whatever conclusion one wishes, simply by deciding which prior publications to cite, and which to completely ignore.
In this case, I suspect two sexually inadequate people found "scientific" support for a conclusion to explain why they couldn't achieve climax. (If I understand the Italian names correctly, one author is male and the other female.)
I may be a 100% gay man, but in my very limited experiences with vaginal sex, I can assure you that there is at least one female creature on this earth that can experience multiple repetitive orgasms from the end of my cock being gently worked against her cervix, notwithstanding the claims of the authors.