Near the end of the Samaññaphala Sutta it says this:
"The king is incapacitated. Had he not killed his father — that righteous man, that righteous king — the dustless, stainless Dhamma eye would have arisen to him as he sat in this very seat." DN 2 https://www.accesstoinsight.org/tipitaka/dn/dn.02.0.than.html
Now in the English language to my knowledge when one uses the word "would" it means something definite. By my understanding it seems that the Buddha according to this sutta is saying that if King Ajatasattu had fulfilled certain conditions such as having not committed such an offense + coming to the Buddha and inquiring etc. as he did in this sutta then the "dustless, stainless Dhamma eye" would have definitely arisen.
So this particular statement seems entirely deterministic unless I am misunderstanding or translation is wrong.
Was the King already a faith follower or wisdom follower?