My initial thought had to do with 'where does masturbation enter the equation with those men not having much if any sex'? I wondered but I haven't read the original research study so I don't know if that variable was considered.
Not to muddy the waters, but waters are never crystal clear - well, they are after you flush the commode - but rarely are things black and white. The study also monitored 3000+ gay males and found that if that population had more than 20 partners their risk of prostate cancer doubled and increased 500% in one type of cancer.
So the answer to the puzzle is not clear - one group has frequent sex and their risk decreases while another group engages in frequent sex and their risk increases. It makes one wonder if one should rethink orgasm denial. But if you live in the US and can't wait to vote for your favorite political candidate in another week - if for no other reason than to finally not have to listen to any more political commercials that distort statistics for the ignorant that listen - then you know that one study proves nothing and that statistics can be interpreted in more than one way.
Here is a link to the scholarly abstract
And here is a link to an article a bit more academic than the 'askmen.com I want to arouse your curiosity' article above.