It has been said that the reason the Buddha did not answer Vacchagotta was because the discussion was not about the doctrine & terminology of the Buddha, but rather about the illogical doctrine of Vacchagotta:
“Sir, why didn’t you answer Vacchagotta’s question?”
“Ānanda, when Vacchagotta asked me whether the self exists absolutely, if I had answered that ‘the self exists absolutely’ I would have been siding with the ascetics and brahmins who are eternalists. When Vacchagotta asked me whether the self does not exist absolutely, if I had answered that ‘the self does not exist absolutely’ I would have been siding with the ascetics and brahmins who are annihilationists.
When Vacchagotta asked me whether the self exists absolutely, if I had answered that ‘the self exists absolutely’ would that have helped give rise to the knowledge that all things are not-self?”
“No, sir.”
“When Vacchagotta asked me whether the self does not exist absolutely, if I had answered that ‘the self does not exist absolutely’, Vacchagotta—who is already confused—would have got even more confused, thinking: ‘It seems that the self that I once had no longer exists.’”
It's also been said that the Buddha did answer the question about what happened to Pukkusāti after a cow killed him even though it was asked by ignorant monks who presumably were - just like Vacchagotta - not using the doctrine & terminology of the Buddha:
But while he was wandering in search of a bowl and robes, a stray cow took his life.
Then several mendicants went up to the Buddha, bowed, sat down to one side, and said to him, “Sir, the gentleman named Pukkusāti, who was advised in brief by the Buddha, has passed away. Where has he been reborn in his next life?”
“Mendicants, Pukkusāti was astute. He practiced in line with the teachings, and did not trouble me about the teachings. With the ending of the five lower fetters, he’s been reborn spontaneously and will become extinguished there, not liable to return from that world.”
This seems inconsistent. Why is it that the Buddha did not answer Vacchagotta, but did answer the monks if both were premising their questions with ignorant understandings of the view of the self?