This seems unlikely to me. Snopes cites an article from the New York Timesfrom 1988 in which William J. Miller, chief editorial writer for The New York Herald Tribune from 1957 to 1959, makes the doughnut claim. Izzard was barely known at the time.
A column in the Times is far more likely a source for Izzard than the other way round.
Well, it could certainly be true that the major source for people repeating it today is Eddie Izzard, not an article in the Tribune from 1988.
Although FWIW, I remember hearing and repeating this tale in high school in the late 80s, early 90s, so it was certainly circulating as an urban legend then.
I had always heard the explanation that Kennedy should have said “Ich bin (ein) **Berlinisch.” **I’ve never taken any German and never known anyone who spoke German that fluently to explain to me what exactly the difference between the two words is, but over the years I’ve inferred that “Berliner” was always the more correct term anyway.
“Berlinisch” is a very awkward adjective. You would recognize it as a word, but there is no situation where “Berliner” would not be the more appropriate adjective. For instance, there is a famous song about the “Berliner Luft” (Berlin air), it would sound very weird with the title “Berlinische Luft”. “Ich bin ein Berlinisch” is right out, that’s not correct German syntax (grammatically equivalent to something like “I am a happy”).
Somewhere in the back of my mind I have a recollection that he did not say “Ich bin ein Berliner” but “Ich bin auch ein Berliner”. Anyway, I read in a notice in a Swedish newspaper that Obama was going to talk to the people of Berlin in the same spot that JFK had held his speech. Unfortunately for the ignorant who wrote it Obama appeared on Pariser Platz in the East of the Brandenburger Tor and JFK was outside the city hall in Schöneberg, which is not even in the neighbourhood of it.