Fair but the article does address this albeit briefly:
"Still, it is unlikely that the high levels of these fatty acids found in the highest quartile would be the result of diet alone. Adults are advised to eat two portions of fish a week, one of them oily, as part of a healthy balanced diet."
You are right that the study doesn't explicitly say fish oil supplements directly caused the high levels of fish oil which were observed in these patients with prostate cancer.
Dailymail at it again :).
