That is the most laughable and stupid comment.
Don't mention it.
You say at the same that it is from Yiddish, you don't speak Yiddish,
I said that? You must have read my mind - in fact I don't speak (more than a handful of words of) Yiddish.
then that you have a Yiddish-speaking ancestry that showed no sign of using the word in that way,
What way? They used it in exactly the current sense of the word (something like "don't care, not interested enough to express an opinion").
but you are making the claim anyway.
What claim? I expressed a preference (not a conviction) as to the (or a?) possible origin of the interjection. My views are pretty much as expressed here.
If the earlier poster (Snowman, IIRC) saying it was around in early 1950s California, it is making my own theory of origin in almost the same meaning with the same sound in Japan most probably correct, spread by the returnfing soldiers.
I heard it as a kid only amongst the elderly Jewish community in Cape Town, where I grew up. Unlikely, I would have thought, that their usage would be much influenced by California slang - except possibly via Hollywood, and I'm not aware of its usage in post-war film.