One cannot be absolute about anything, but maybe a little further detail, without going into the whole of recording history, might be helpful to you.
‘To absolutely nullify the possibility’ “acetate” or more correctly cellulose nitrate lacquer recording was not available until 1932/3 so Rudolf Steiner [RS] would not have been able to make such a thing. If it was RS then he would have to travel to the Paris studios of Pathé to make a recording onto a master cylinder, this would have been transcribed by a pantograph to a disc master from which stampers and pressings would result. Even if RS had managed to get to the studio, and had made a private electric recording, he would have to have managed this in the last months of his life, unfortunately Pathé did not have electrical recording this early one so it would be therefore be an acoustic recording he made for them. As George has said it is more likely to find him speaking in Archives de la Parole around 1913 or so.
If we deconstruct the argument that RS could have made recordings during the acoustic period of technology, then Pathé and RS must have kept this very quiet and then Pathé did not bother to issue the recordings until seven years after his death, unfortunately no documentation that RS ever put his head into the Pathé recording studios has survived, or been discovered to date, or maybe it was all done secretly and the paper trail carefully destroyed. Then in 1932 Pathé decides to transcribe these master cylinders, via an electrical method, and issue them without any fanfare.
They also decided to just slip them out on a standard Pathé label in the middle of a matrix series that was cut early in 1932, probably during a quiet moment at the studios when they dusted of a cylinder in the archives between the recording sessions of Arthur Endrèze matrices 250238/9 Cat. No. X90040 and Paul Franz matrices 250242/3 Cat No. X90043. They then pressed records for sale, hardly made any fuss of them, and issued them probably about June 1932, since when nobody has noticed them or commented that they could by RS and indeed ever since nobody has even thought to make the link.
Roughly at the same time at Paris there just happened to be a singer with the same sort of name, maybe just a coincidence. Some digging in French journals and newspapers may yet identify him more accurately, this research may even show that contemporaries were completely mistaken in thinking he was the same singer who sang so well at the Trocadero the previous year, and not some cleverly re-engineered unissued recordings by RS issued in order to fool the critics and pubic alike.
I jest of course, but I think that you really need to find evidence to disprove that the recordings are not by Rudolpe Steiner who sang at Paris in 1931; and further, and more to the point, find some substantive evidence that Rudolf Steiner actually made these or any recordings.