Weird Movie Theater Food Habits (8 pics)

It's a southern thing.
People used to drink vinegar in hot weather - think about what gatorade would taste like without any sweetener - so tastes in the south are often about 'vinegary' flavours. BBQ has vinegar in it, too.

I'm guessing it started in the days before air conditioning in theaters.

In 1925, Willis Carrier installed a "refrigerating plant" in the Rivoli Theater in Times Square, ushering in an era of air conditioned summer entertainment.
In the early days of movies, the promise of “air conditioned comfort” helped many 1920s theater owners improve summertime box office receipts. Prior to air conditioning, however, crowds typically shunned hot theaters for cooler pleasures.
According to Carrier Corp., “The world started to become aware of air conditioned theaters when Carrier brought a centrifugal chiller to the Rivoli Theater in New York’s Times Square in 1925.”