I too have experienced the same "belching popcorn" taste, and usually the next morning, I will have a diarrhea very bad. No pain in the guts, just a poop of about a gallon of the 'chocolate milkshake' shitz.
Can be bacterial overgrowth in your gut, or if he have ate a lot of acidic foods. Try drinking lots of water to help flush the bacteria out, will also help with dehydration caused by diarrhea. If it persists you can go see a primary care physician as it may require antibiotics if the body is unable to flush itself of the underlying cause. If you have ate anything high in protein recently that could be the culprit as well, as when proteins are broken down in the stomach the gut bacteria produce hydrogen sulfide, hence the silver burps.