I read someone else's post explaining how as Ezio was dying he basically hallucinated himself as a young man there since in the end you get the credits “when i was a young man I had liberty but did not see it, I had love but did not feel it” and so on, plus how the man says courage Ezio, before leaving, and would explain why Ezio confronted him with “I don't think its the women that are the problem”
Also for the theory he was posioned, ezio showed signs through out the mini movie, of being on deaths door from simple old age, and right before going to the plaza were he dead, before his wife came in his office like room, he showed signs of a heart attack and then again in the plaza, exio died of age from a heart attack, natural death
I dont want credit for discovery of who the man was so heres the site were i learned it: