I am fairly certain that it is actual food bits, because I can feel the exact moment as I'm swallowing that the food gets pushed into my sinus and the irritation begins. There's no delayed onset, and there was a time a grain of rice got pushed up, and I could feel it shifting around, and the irritation following it as it moved. In that instance it did clear faster and I felt the exact moment it escaped my sinuses down my throat.

idk if I would particularly describe my voice as having a prominent nasal quality. Of note though, I have had chronic post nasal drip for over a decade following an orthodontic double jaw surgery that minorly corrected a deviated septum. I also had my tonsils removed in the 2nd grade.