I never heard that before.
Thinking of people I know, my dad's United, the rest of his immediate family's City, and the family up there in general is pretty much split. The only other Manchester Jewish family I know are City.
It could be simply that City were the glamour club up until the late forties United were the "rags", so they had more support generally? I don't know to be honest.
In Glasgow, where there's also a large Jewish population, the majority support Celtic but not by that much, surprisingly given Rangers' fascist links. It may be that some have drifted away from Celtic since they started bringing out Palestinian flags...and Rangers have followed suit with Israeli ones.
spastics