If it wasnt still the shape of a mouse then its not regurgitation, one thing I noticed is you said you picked him up to put him back in the enclosure after eating. Why arent you feeding him in the enclosure? Also do you notice its mouth open slightly all the time, like its breathing with its mouth open?
Almost all of my snakes take a gnarly dump after a shed, I find the skin and then a huge pile next to it...