I don’t know why he did it either. I can only assume it was a mistake.
There are people from New York in many places that are not New York, so I don’t really see how it benefits him to paint with a broad brush like that.
It strikes a chord with folks that would turn-up their noses at Salsa made in New York City !! The same folks who wouldn’t give a thought to buying a Toyota, Lexus, or Nissan made in Seoul, Yokohama, or assembled in Marysville, Ohio from parts imported by container from the far east. It was a crude attempt to dredge-up indignation for a cheap political point.
Unfortunately, Senator Cruz miscalculated and probably handed New York State to Mr. Trump.