That same discussion … that someone has poisoned me.
( S.P.Room Conversation November 10, 1977, Vrndavana )
Srila Prabhupada is saying he has been poisoned, not 
That same thing …that someone could have poisoned me or
That same thing … They say that I've been poisoned or
That same thing … Someone says that I've been poisoned. It's possible"
The conclusion of that previous "same discussion- thing" is now given from the lotus mouth of the Acarya Srila Prabhupada.
someone has poisoned me
 It is also clear from the following statements by Tamal Krishna and the Kaviraja, ( made after Srila Prabhupada said someone has poisoned me) that they understood that Srila Prabhupada was now clearly stating what was been previously discussed as a possibility.
Tamala Krsna: Prabhupada was thinking that someone had poisoned him.
Adri-dharana: Yes.
Tamala Krsna: That was the mental distress.
Adri-dharana: Yes.
Kaviraja: (Hindi)
Tamala Krsna: What did Kaviraja just say?
Bhakti-caru: He said that when Srila Prabhupada was saying that, there must be some truth behind it. (People all speaking at once)
Tamala Krsna: Srila Prabhupada, Sastriji says that there must be some truth to it if you say that.
So who is it that has poisoned? (pause)
( S.P.Room Conversation November 10, 1977, Vrndavana )