Most sources say it was forced suicide. It makes sense given the recent events in that time-line and yes, it makes sense with Cao Cao. The man was ruthless, very very ruthless. The man buried alive an army, massacred a considerable part of a province, hunted down a childhood bully to lands even further south then Wu. He executed some very loyal officers like Cui Yan. So why not Xun Yu if he becomes a threat?
“You, are a rebellious son who abandoned his father. You are a cruel brigand who murdered his lord. How can Heaven and Earth put up with you for long? And unless you die soon, how can you face the sight of men?”