“Bhikkhus, an instructed noble disciple does not think: ‘When what exists does what come to be? With the arising of what does what arise? [When what exists do determinations come to be? When what exists does consciousness come to be?]132 When what exists does name-and-form come to be?… When what exists does aging-and-death come to be?’
“Rather, bhikkhus, the instructed noble disciple has knowledge about this that is independent of others: ‘When this exists, that comes to be; with the arising of this, that arises.
SN 12: 49
But of course regarding future appearing of the new body in the field of consciousness we may say that Venerable Sariputta has no any such direct knowledge, so you are justified to say that he "inferred it:
But, Sāriputta, if they were to ask you: ‘Friend Sāriputta, through what kind of deliverance have you declared final knowledge thus: “I understand: Destroyed is birth, the holy life has been lived, what had to be done has been done, there is no more for this state of being”?’—being asked thus, how would you answer?”
“If they were to ask me this, venerable sir, I would answer thus: [54] ‘Friends, through an internal deliverance, through the destruction of all clinging, I dwell mindfully in such a way that the taints do not flow within me and I do not despise myself.’ Being asked thus, venerable sir, I would answer in such a way.”
“Good, good, Sāriputta! This is another method of explaining in brief that same point: ‘I have no perplexity in regard to the taints spoken of by the Ascetic; I do not doubt that they have been abandoned by me.’”
SN 12: 32
In other words Venerable Sariputta has a direct knowledge:
‘This field of perception is void of the taint of sensual desire; this field of perception is void of the taint of being; this field of perception is void of the taint of ignorance. There is present only this non-voidness, namely, that connected with the six bases that are dependent on this body and conditioned by life.’ Thus he regards it as void of what is not there, but as to what remains there he understands that which is present thus: ‘This is present.’ MN 121
Whether “this non-voidness, namely, that connected with the six bases that are dependent on this body and conditioned by life” will be replaced or will not be replaced by another body without supernormal powers, you are right, arahat only inffers.
And I inffer, that it doesn’t matter, since it is enough to know:
I have no perplexity in regard to the taints spoken of by the Ascetic; I do not doubt that they have been abandoned by me.’”
Definitely ven Nanavira is right when he says:
ariyasàvaka has direct, certain, reflexive knowledge of the condition upon which birth depends. He has no such knowledge about re-birth, which is quite a different matter.
Q: Yet, you must believe in having lived before.
M: The scriptures say so, but I know nothing about it. I know myself as I am; as I appeared or will appear is not within my experience. It is not that I do not remember. In fact there is nothing to remember. Reincarnation implies a reincarnating self. There is no such thing. The bundle of memories and hopes, called the ‘I’, imagines itself existing everlastingly and creates time to accommodate its false eternity: To be, I need no past or future. All experience is born of imagination; I do not imagine, so no birth or death happens to me. Only those who think themselves born can think themselves re-born. You are accusing me of having been born — I plead not guilty!
M - Nisargadatta Maharaj