Yes, this has a lot to do with Dysbiosis and probably SIBO.
An increased BUN level is often associated with a decreased production of hydrochloric acid in the stomach (hypochlorhydria). Why? Because hypochlorhydria leads to poor protein digestion in the stomach. This leads to increased levels of undigested protein in the intestines and greatly predisposes one towards the development of a dysbiotic bowel with an overgrowth of bacteria.
Putrefactive action of this bacterial overgrowth on the excess nitrogenous waste releases significant quantities of ammonia. Some of this ammonia will be converted into urea by the liver. Increased bacteria in the colon will also metabolize urea often leading to an increased BUN.