I've never heard of anyone having issues with pretzels but I know popcorn can cause me to reflux especially if it's of the movie theater variety. Chances are though that it's the butter/grease on the popcorn that is causing my issue.
The best way to determine if any food is causing you an issue is to keep a food and symptom log. It's very difficult to remember on a daily basis what you ate and what your symptoms are but if you are able to keep a log about it you may be able to see trends.
Good Luck - Stephanie