Here is Bhikkhu Bodhis' summary of the commentary's take on this story:In the past, it is said, five hundred men earned their living together as hunters. They were reborn in hell, but later, through some good kamma, they took rebirth as human beings and went forth as monks under the Blessed One. However, a portion of their original bad kamma had gained the opportunity to ripen during this fortnight and was due to bring on their deaths both by suicide and homicide. The Blessed One foresaw this and realized he could do nothing about it. Among those monks, some were worldlings, some stream-enterers, some once-returners, some nonreturners, some arahants. The arahants would not take rebirth, the other noble disciples were bound for a happy rebirth, but the worldlings were of uncertain destiny. The Buddha spoke of foulness to remove their attachment to the body so that they would lose their fear of death and could thus be reborn in heaven. Therefore he spoke on foulness in order to help them, not with the intention of extolling death. Realizing he could not turn back the course of events, he went into seclusion to avoid being present when destiny took its toll.
So the commentary, but the idea of a kammically predetermined suicide seems difficult to reconcile with the conception of suicide as a volitionally induced act.
Thanks for that.
All I can say, that's an unsatisfying explanation...