The incident that Manfred is referring to, admittedly a rather troubling one, is to be found at Vinaya III,68-71. Most scholars agree that the Vinaya in its present form is significantly later than the four Nikayas and its language, structure and the historical data it contains all confirm this. When we look at the mass suicide story the first thing we notice is that like many stories in the Vinaya it is formularistic, which suggests that it is artificial. We also have to consider the context in which the story is found. It occurs in the third part of the Parajika which deals with murder. Each situation or behavior that would or might be considered murder is illustrated by a story. Some of these stories are plausible and may have actually happened, others are rather forced and implausible. The mass suicide story looks very much like it has been constructed as an excuse to make a rule concerning encouraging a person to kill themselves or to assist them in killing themselves, rather than being an incident that actually happened. Can we really believe that 60 monks (that’s what the story says) a day killed themselves simply by doing the meditation on the repulsiveness of the body? So I would a suggest that the mass suicide is illustrative rather than actual.
Now we come to the second part of Manfred’s question – Was the Buddha really a ‘teacher of gods and humans’, could he really foresee the destinies of other beings making him a perfect teacher? Certainly the four Nikayas portrays the Buddha as an exceptional skillful teacher and I have no doubt that this portrait and the many examples of this teaching skills are authentic. I even believe that his wisdom was so sharp and his understand of the human psyche was so profound, that he was often able to know exactly what was best for a person as far as meditation. In fact, it was probably this ability that gave rise to the belief that the Buddha could unfailingly read everything in the mind of every person who approached him.