It''s true. I've noticed this a lot on my trips there.
One time we went to a bbq joint and ordered a platter and literally everything on it was sweet. The meat, the coleslaw, the beans, the macaroni salad, the vegetables and the lemonade was the sweetest thing I've ever had.
If you go to fine dining joints though, they are usually fine. It's most just the cheap and mid-tier stuff that's sweet.
Well BBQ differs greatly depending on where you get it, and the quality of the restaurant. Kansas City BBQ is usually associated with a lot of sugar and sweetness. I hate it. Vinegar or mustard based sauces are generally associated with the southeast, but it breaks down differently depending on the states, and even within the states there are different tastes.
I'm more of a Memphis style BBQ fan, but most of it's great so long as it's not sweet. My BBQ has a good Memphis style rub, but the sauce I make is my own concoction and I have no clue what region it would be more like. Has ketchup, hot sauce, apple cider vinegar, mustard, little brown sugar, pepper, salt, and a little garlic.